Well, my thank you to everyone for listening to the webinar tonight, and my thanks to Verva for inviting me to speak and to Webinar vet for making that possible. Tonight we're going to have a good overall review of Mar cell tumours. I'm gonna start with a little bit of the biology of Marcels.

We're talking more about Mar cell tumours in general and particularly emphasising my approach to them clinically before reviewing the treatment options. So mast cell then are the body's emergency responder cells. OK?

You find these guys at the boundaries between your body and the outside world, and they have a pivotal role in controlling the response to harmful external stimuli. So in more detail, mast cells are a specialised type of white blood cell, and they're born as an immature precursor in the bone marrow. But they develop to the functional mast cells in the tissues under the actions of stem cell factor.

And it's not just any old tissues you find them in, you find them in the connective tissues of the skin and the subcutis. And around blood vessels, and in even higher numbers in the mucous membranes or the lining of the gastrointestinal tract. That is the places where you're likely to encounter external antigens.

And specifically, mast cells have a very, very key role to play in the response to parasites, in the response to insect venomation and induction of the innate immune response. And let's consider these things a little bit more, because all of these things need to be very, very quick, OK? The reason why the innate immune response exists as a stereotyped response is so it can be rolled out very quickly to neutralise pathogens and to get tissue healing under way before the time the acquired immune response is able to take over.

So, and it also goes without saying that response to venomation and response to parasites also needs to be quick. So speed is of the essence. And here we have a bit of a conundrum.

Because when things like the, these inflammatory responses get going, you'll need to change the homeostasis of the tissue dramatically from quiet equilibrium. We will need to facilitate ingress of lots of different types of white blood cells and to activate them. You'll need vasodilation, increasing vascular permeability, and increase in the level of protonnaceous fluid in the environment.

And to orchestrate all these things, you'll need a very carefully coordinated release of chemical mediators, and to induce this will take a lot of time. So here, ladies and gentlemen, we can explain an essential feature of the Marcel biology. They are preloaded with granules of these inflammatory mediators, so that they can be released in a split second upon stimulation.

And if you look at the cytology here, these granules of the inflammatory mediators and lots of other chemical messengers, give them our cells their characteristic granular appearance. So, in more detail again. The mast cells will degranulate and release these granules on stimulation by physical stimuli, chemical stimuli, either exogenous or endogenous, rapid temperature change or immunological stimuli.

And this feature of the mast cells to release all these chemical messengers into the environment. It it can explain two types of pathology we commonly see. In the first, there's type 1 hypersensitivity, the common allergic response or urticaria we may see.

That's when the mast cells are bound by immunoglobulin that have bound themselves and allergen. And the subject for today in mast cell tumours, you know, tumours are characterised by uncontrolled cell division. And so, being out of control, sometimes mast cell tumours will release these chemical mediators for no apparent reason, or after very, very minimal upset.

So that brings us on to mast cell tumours. And there's lots of statistics around these. I'm sure we've all seen mast cell tumours, but they're very common.

They're up to 20% of canine skin tumours, and people have even calculated at least 12 cases per veterinary surgeon in the UK. Quite commonly in up to another 50% of cases, they may occur as multiple lesions on the same dogs. All mast cell tumours are within the brackets of cancers.

A lot of these we can cure, a lot of these are great prognosis, but they're all cancers, and as cancers, detecting them early, will help you get a positive outcome. We see mast cell tumours much more commonly in certain breeds, often the popular breeds like Labradors, golden retrievers, savageable terriers, fine marans, etc. And all the brachycephalic dogs.

They can occur in any dog, however. They're most prevalent in dogs of middle age or upwards, but you can see them in dogs really quite young, just a couple of years old. And there's no gender association or no effects of neutering.

Now mast cell tumours look like this, OK? In other words, they can look like pretty much anything. And I would say that you could never discount the possibility of any cutaneous or subcutaneous mass being a mast cell tumour.

They can occur on any part of the skin or the subcutis, and of course, you can get them on the mucous membranes and in the gastrointestinal tract, as we discussed. Now, a lot of the ones on the skin or subcutis tend to occur in awkward locations, like on limbs or the muzzle, and that can make surgery difficult as we're going to explore. And as I alluded to, mast cells are packed with chemical messengers that can be released in a split second notice.

And principally, these are things like histamine, heparin, proteolytic enzymes, cytokines, and growth factors. These things that we said have a very, very important physiological roles, but in the case of mast cells, you can have much more of them, for no apparent reason. Again, these are cells that are not in mast cell tumours rather, are not under the body's control.

And so we commonly see effects of these things degranulating. The local effects that you might see after FNAing or handling a mast cell tumour could be characterised by redness, swelling, or itchiness in and around the mast cell tumour. This is the Darius sign.

If you cause degranulation at surgery, it can also slow down the wound healing. Much less commonly, you can get sufficient release of these chemical messengers into the circulation, and you can cause systemic effects like vomiting, diarrhoea, gastric ulceration, hypertension, shock, fever, peripheral edoema, and coagulation abnormalities. Now, to get these systemic effects, you typically need a lot of these granules to be degranulated, and that often correlates with a large burden of tumour.

So fortunately, the systemic effects are rare, but the local effects are quite common and often seen after just physically manipulating a mast cell tumour. They can also be the reason why a lump may be reported to swell up and go down again in the history. To diagnose a mast cell tumour.

High quality, fine needle aspirate is all you need, OK? And often they can look a bit like this, where you've got very, very purple cells with lots of purple granules within them, often obscuring the nuclear detail. Remember that these are all cancers though, cancers don't have any rules to follow.

They've escaped the body's control, so sometimes they can look much less differentiated, and you might see things like this, like weird mitotic figures. Bizarre nuclei. Multi-nucleation, or marked variation in shape or form of the nuclei.

And notice that all these less well differentiated mast cells have much fewer granules. So on occasions it can be a difficult thing. Now I think everyone in practise should perfect a good fine needle aspiration technique.

And Verbach have provided this slide here with some beautiful images on how to aspirate with a syringe attached using negative pressure. I actually don't use this. I use a needle on its own, and then I attach the syringe just to squirt the material onto a slide.

But I'm not saying that one technique is better than the other. Try them both yourselves. Mark the slides, which one you've done with each.

Send them to the pathologist and see what the pathologist says gives you the better sample. So find out which one works for you. And after we've diagnosed the mast cell tumour, the next steps can be quite variable.

OK? And understandably, this results in a lot of confusion with veterinary surgeons and, and also me on occasions. Because the fine needle aspiration tells you, is this a ma cell tumour?

Yes or no? The prognosis of the mast cell tumour and its likelihood to spread to other parts of the body is often dictated by the histopathology, plus minus other prognostic factors like high 67. OK?

And we don't tend to get the histopath until the tumor's been removed in a lot of cases. So do we want to stage the tumour first to see if it's spread? And navigating this step of the mast cell tumour can often create quite a lot of confusion.

I would encourage people to make sense of it with two questions. Is there a high risk of metastasis or aggressive behaviour from the information that we already have? That is from history and clinical exam.

And secondly, is the tumour amenable to complete surgical excision with appropriate margins? If you think in terms of these two questions, the problem will be much simpler. So for a lot of mast cell tumours, in fact, the majority of cutaneous mast cell tumours, you can do this.

OK? That is if there is no concern from the history and clinical examination that this is gonna be an aggressive tumour and complete surgical excision with margins is attainable. For now after fine needle aspirate, I would proceed to remove the tumour with appropriate margins.

Sometimes, based on the histopathology, you get a nasty surprise. And it looks like a more aggressive tumour than you'd thought, and you might need to go back and do staging later. But I still think that's an acceptable way of doing things.

And sometimes after the histopath, you're a bit unsure, and you might need other prognostic indicators like K 67 or CCI mutation. And you could run those and then decide whether the staging is needed at a later date too. Now, if there's concerns present on history or physical exam that this is gonna be a really aggressive mast cell tumour, you might be justified in staging it first.

And then talking about surgery later, OK? The other instance you could do this is if surgical excision's going to be difficult, expensive, or a radical procedure. I think you should stage it first as an insurance policy to make sure that the effort and expense of surgery is justified.

And in these cases, I would also try to get an incisional biopsy of the tumour at the time of staging. Just to get as much information that this is going, that surgery is justified as possible. OK?

And again, after the histopathy, we may revert to prognostic factors if possible. So in approaching a mast cell tumour, I think two questions are key. Is there a high risk of metastasis or aggressive behaviour from the information we have to hand?

And is complete surgical excision possible. Now, 0.2 here is more intuitive for you and I, isn't it?

We can get this from physical exam, appearance, location of the lesion. But I think deciding whether there's a high risk of metastasis is a harder thing, and I'm going to discuss my approach to this just now, OK? I would encourage every vet dealing with mast cell tumours to categorise the mast cell tumour as high risk of metastasis or low risk of metastasis from the start.

Now, often you don't have the strongest information, you don't have the histopath to start with, so you have to make a provisional categorization. And you have to tell the owner. That you may change this after you get the histopath at a later date.

So my, many things have been published as correlating with an aggressive Mar cell tumour behaviour, but I'm gonna run through some of the things that I think are most important. The first one is the GASP test. OK.

If you look at a tumour across the room and you go. And it's bad. So more specifically, the abnormally large, the rapidly growing, the severely ulcerated ones.

0.2 tumours in certain locations of the body like the prepus, mucous membranes, scrotum, muzzle, they tend to correlate with more aggressive behaviours. Number 3.

The Sharpei breed is reported to have a much higher proportion of the aggressive mast cell tumours, than the less aggressive ones, so I'd take a mast cell on a Shar Pei very seriously. If there's obvious local lymph node metastasis. It's a fairly easy one.

If there's systemic signs of vasoactive amine release or chemical mediator release, now that I think is an indirect effect that requires a bit of explanation. Because every mast cell tumour in the world can degranulate. But those that degranulate to the extent of causing systemic issues like this poor dog here, or the swelling of the leg here, they're usually the mast cell tumours that have got to a very, very large cancer burden.

And how have they got to such a large burden? Often through metastasis. And finally, we often forget this, but incompletely cut mast cell tumours don't always recur.

In fact, some reports say more than half of them don't recur. So the mast cell tumours that choose to recur after an incomplete excision are a nastier breed of mast cell tumour, and we need to be aware of that. So from history and clinical exam, these 6 things would be some of my top worries.

Now, after we've got either a biopsy or remove the tumour, we can get things like the grade, OK? And be aware that there's at least 2 grading systems commonly used. They're both based on histopathology and they're both evaluated for cutaneous mast cell tumours only.

The grade is very, very prognostic. If you haven't seen many of these survival curves before, it's very easy. On the Y axis you have 100% of dogs alive up here, 0% of dogs alive here against time.

And it follows that the tumours with a better survival will have to curve near 100% for longer. And those with the poorest survival have the curve getting towards 0 sooner. So you can see here that grade 1 patnick Mar cell tumours have an excellent prognosis and don't die.

Grade 3 mat cell tumours have an average survival of about 6, 10 months, whatever. OK, it's a very, very prognostic. So we can see that this blue line, the patent grade ones, and this green line, patent grade threes, a very clear prognosis.

And on the pupil system, again, the green line, the high grade tumours have a clearly bad prognosis. If you look at Patnick Intermediates. Or the low grade pupil.

Some of these dogs will die. Some of these tumours behave like an aggressive tumour, but others behave like a non-aggressive ones. And the frustrating thing is that these red ones here are the majority of my cell tumours that you and I will see.

Another criticism of the grading system is that particularly the patick one can be subjective and can have a lot of inter-pathologist disagreement. There's less inter pathologist disagreement with the Cupil system, but it's not quite as well evaluated. So, things on the path report that would worry me and put this tumour in a high grade, confirm it as high grade or move it, sorry, as high risk or move it from low risk to high risk would be first, the high grade, because that's always bad.

But most mast cell tumours are intermediate grade, and could be either. And for these intermediate grade tumours, I'd encourage you to look at the mitotic count in the first instance, potentially also using Chi 67. That is because mitotic count and K 67 have been shown to be prognostic in many studies, and furthermore, their significance is independent of other variables like grade or things like that.

So these are tremendously useful things, and with every intermediate patick tumour or low pupil tumour, I'd look at the mitotic count first, and then K 67 if they're still concern or equivocal. You've also got things like agor, CI mutation, key kit protein staining. You could run these.

They have been shown to be prognostic, often in several studies. But we're still not sure whether their prognostic significance is independent of things like grade yet. So I would put them as possibly a bit less important.

So some people ask me for examples of where I would run these extra prognostic tests, like I 67, AgO, CIC, I67. I think there's 3 situations, really. First is where you've got a patternic intermediate grade ma cell tumour, where the mitotic count is just under the cutoff of 5 in 10 high power fields, where you'd worry about aggressive behaviour.

So if it's 4 or 3, I might run them there. I would also consider these where you've got . Contradictory information.

For example, a tumour on a prep use would normally correlate with very aggressive behaviour, but you might have a pathology report that suggests a very indolent course of behaviour, and you want to know whether you need adjunctive treatment in this dog or not. And the third situation would be things like subcutaneous or mucous membrane mass cell tumours, where the grading system is just not validated, and I want to get as much information as I can. So, I would tend to request K 67 in the first instance, because that has independent prognostic significance, and I feel it is more important than the other other factors.

But there are situations, particularly where I want as much information as possible, where I might run the full panel. That's just my choice, though. And so it's a bit awkward with Mar cell tumours, isn't it?

Often we've treated the dog, we've done the definitive treatment to get rid of the Mart cell tumour before we find out whether we need to worry about it metastasizing. And it's a bit backwards, and we need to counsel the owners that we may change our tune a little bit after we get the pathology report. It would be nice if we could get information on the likelihood to metastasize before going to surgery and doing the definitive treatment.

And so there have been numerous attempts over the years to develop a grading system based on cytology. And this one poses the most promise. It's released in 2016.

And they showed some very good accuracy data actually, compared to histopathology. OK? With this kind of sensitivity.

It will miss 1 aggressive mast cell tumour in 10. And with this kind of specificity, it will give you one false positive for an aggressive mast cell tumour in 20. So it's not perfect, but it's still pretty good.

It's the best attempt on cytology, and I think it could potentially be very useful. What we'd like to see is how well it transfers to other pathologists and how the other pathologists are able to implement these rules in this paper and whether they get such good data as as the authors here. But I think it's a very interesting publication and I'd like to see it better evaluated.

The other thing that you can do based on cytology alone is assess the CI mutation, OK? Now, mast cell tumours differentiate from the precursor into the what we know as the proper adult mast cell, under the action of stem cell factor. And a proportion, a significant proportion of our cell tumours are malignant because of a mutation in the CIt gene coding for the kit receptor in the cell membrane.

So around 1/3 of mast cell tumours have a kit mutation, driving the malignancy, driving the malignant effects. And knowing that the CIP mutation is present may help us to choose appropriate drugs if we're gonna use drug therapy. But importantly, from a prognostic point of view, these tumours with the CIP mutation tend to be the more aggressive ones.

So, I mentioned this test because it's a PCR test, and you can run it from cytology. You can run it on stained cytology slides that are already at the lab. So if you want more prognostic information from cytology, please consider asking the pathologist to apply the Causs grading system and consider requesting a C mutation from the slides.

So staging of my cell tumours then. Put this slide up, because this shows the WHO staging system for canine mast cell tumours. Now, I wouldn't want anyone to pay an awful lot of attention to this because I don't tend to use it in the clinic very much.

It's just useful for reference when you're reading papers or textbooks on Marcel tumours, because often the tumours will be staged in these publications, and quite rightly. I'm gonna share with you my approach to staging a mast cell tumour right now. Before we stage a tumour.

We need to have an idea of how it's gonna behave if it's very aggressive and it spreads, OK? These are the solid tumours. They're the sarcomas, the carcinomas, the melanoma, and when they spread, they form other solid tumours.

OK, it's quite easy to spot. Lymphoma, leukaemia, myeloma are the liquid tumours, and that is they're systemic diseases really, and we don't often talk about metastasis, but when they infiltrate other organs. They do so often quite insidiously, and it may be that the organ is a little bit distorted in shape or a little bit enlarged or it may be, it looks perfectly normal.

So to see if one of these liquid tumours has infiltrated an organ, you need fine needle aspiration. So what for mast cell tumours then? Do they behave more like the solid tumours or the liquid tumours?

What do you think? Actually, they're quite annoying because the primary tumours tend to behave like the solid tumours. And we talk about surgery and margins and completeness of excision.

Now when mast cell tumours spread, they behave more like the liquid tumours. OK? They will infiltrate organs insidiously, and you may not know they're there until you sample them.

So when we're staging mast cell tumours, it may seem quite complicated because of this kind of duality and behaviour that we have. But due to one feature of the mast cell tumours, staging can be quite simple. And that feature is that mast cell tumours metastasize quite reliably through the lymphatics, going into draining lymph node, often further lymph nodes, the liver, and the spleen.

So I can offer you quite a simple approach to staging mast cell tumours. You assess the draining lymph node, the first stop in the lymphatic chain. And then you assess the liver and spleen, but often the last stop in the lymphatic chain before the lymph enters the circulation.

And of course, because it's behaving like a liquid tumour now, you're going to need to aspirate things to know whether there's mast cell tumour in them. And I intend to prove that to you in a minute. So just a reminder, this is a reactive lymphoid population, lots of lymphocytes, lots of shapes and sizes.

And this is what a mast cell tumour looks like when it's effaced a lymph node. This is also a mast cell tumour that's metastasized to a lymph node, but the cells are much less poorly, much less well differentiated, and they don't instantly look like mast cells. Now when you assess the draining lymph node, you need to consider where that lymph node may be.

Because frustratingly, it's not the anatomically most proximate node in 40% of cases. Therefore, in practise, I would look at several candidate lymph nodes and aspirate all of them. For example, for a tumour at the distal left hind, I might choose the popliteal, the inguinal, and the medial iliac node as the candidate nodes, and I would use ultrasound to aspirate them if needed.

A cleverer way, usually a referral procedure though, would be with sentinel lymph node mapping. And I'm pleased to say that's something we offer in our hospital using a CT scan, injecting contrast agents subcutaneously around a tumour and tracking the lymph node that the contrast moves to over the next 10 minutes or so. And sentinel lymph node mapping is a very, very powerful technique, because in this paper here, out of 20 dogs, they found mets in lymph nodes where they wouldn't have expected them in 8 dogs.

And these 8 dogs got offered therapies that they otherwise would not have been offered. So for the committed client who's well funded, referral for a procedure like this can be really, really useful. In assessing metastasis distantly to liver and spleen, I've now got a question for you, OK?

This is normal liver, a little bit darker than the spleen. This is hyperrechoic liver. A bit brighter.

And this is hypoechoic liver and you can see the kind of biliary vessels are lighter than the liver parenchyma. Which one of these is the one with the metastatic mast cell tumour? Have to think this to yourself.

The answer is all of them. OK? And this is normal looking spleen.

This is kind of mottled honeycomb type spleen. Which one of these two has got the metastatic mast cell tumour? And of course the answer is both of them.

OK, and it's not just from this publication, there's others agreeing with it as well, that if you just look at a liver and try to decide whether it's got metastatic mast cell disease in it or not, from looks alone, you'll miss every single case. Every single one, ladies and gentlemen, the sensitivity is 0%. It's a little bit better for the spleen, but you'll still miss about 60% of cases.

So we don't really look at the parenchyma of these organs, we just sample them. The involvement of the mast cell tumour is often diffuse, and sampling is quite a sensitive way of finding that. A lot of people X-ray the chest when they're staging a mast cell tumour, and you're not wrong for doing that at all.

But you're certainly more very, very unlikely to see lots of pulmonary nodules with a metastatic mast cell tumour. The reason why I might image the chest in staging a mast cell tumour is to look for this, OK, in large lymph nodes. If the mast cell tumour is on the front half of the dog, the draining lymph node may be in the thorax.

So I would image the thorax to look for enlarged lymph nodes there. And so now, to bring this section on my approach to a mast cell tumour together, I'm going to give you a few, a simple algorithm, if you like. I would consider not doing many staging tests at all.

If the tumour seems to be low risk of metastasis from the information you have to hand. And an appropriately large surgery is feasible without expensive or radical procedures. I'd of course, counsel the owners carefully, but I may change my mind about this.

I may say we need to stage later. I may say we need chemo later. I may say it has a poor prognosis later.

So we'll need to make sure that they're well informed. But when I talk about minimal staging, I talk about my thorough physical exam. Find any other mast cell tumours that are going on, you should be able to find them in up to 20% of cases.

I'd do bloods and urine and blood pressure if needed, as you know, at my, at the vet's discretion really for safety for general anaesthesia. And where possible, I'd sample the local lymph node. And that's all I do.

Take the ma cell tumour out then. And this approach, approach number one should apply to most mar cells that you see. If I think there's a high risk of the mast cell tumour spreading, I would do the minimal staging and I would also do ultrasound of the area, the sentinel lymph node candidates and FNA the lymph nodes, liver and spleen.

If the tumor's on the front half of the dog, I would also image the chest looking for enlarged lymph nodes there. If I was staging a tumour because I was worried, not so much about the tumour, but just the location it's in, making it difficult for surgery. I would also take a biopsy of the tumour to make sure we have as much information as possible before going for the expensive or radical surgical procedure.

And there's a variation on the approach to the high risk mast cell tumours, you could consider sentinel lymph node mapping, instead of the ultrasound and aspiration speculatively of several lymph nodes. So the end result I'd want to have is knowing that a tumour is non-metastatic, regionally metastatic or distantly metastatic. And it's these three categories that I tend to think about.

The WHO system dictates. Some people ask, why am I bothered with regionally metastatic versus distantly metastatic, because if it's spread, it spread, and that's bad, right? Well, not really.

Because if you have a patnic intermediate grade mast cell tumour that spreads to one lymph node. There's a good chance it can be cured. OK?

And this is probably a feature of mast cells being white blood cells. They find it easy to get sucked into lymph nodes and easy to proliferate in lymph nodes. But if the mast cell tumour itself isn't too aggressive, there's a good chance they may just stop at one lymph node.

So, in this paper, and a couple of others now, we saw long term survival in dogs with patnick grade 2 ma cell tumours that metastasize to one lymph node only. But to get this survival, you do have to work hard, I'm afraid. You do need to remove the primary tumour and either remove or irradiate the lymph node, and then you need a course of chemotherapy.

But it's worth doing because you can cure these guys and it's not often in veterinary medicine we talk about curing metastatic cancer. OK. So now I'm going to review the treatment options in the final parts of my talk.

And the best place to start is with surgery, OK? Surgery is the curative treatment for at least 80% of mast cell tumours. And really, at least up to now, it's been the only definitive treatment we've had for these mast cell tumours.

For a low risk mast cell tumour. My surgery alone, be my recommendation. And if it's high risk, I'd still recommend surgery, but it's gonna be high risk of metastasis, so we need adjunctive medical therapy to stop this.

And with the low risk ones, I hope you'd cure with them and that's about 80% of mast cell tumours. And even if it's a high risk mast cell tumour, they have been shown to have a better prognosis where the local tumour, local tumour control has been achieved, as well as chemotherapy has been given. Some people think you could just give chemo to these, but often that doesn't take into account the morbidity that can be caused by a high grade mat cell tumour left in situ.

So, that's possibly a bit simplistic. You do have to take into account the initial people and the funding that they have and also the specifics of the dog. But ideally, I'd go for surgery for all my cell tumours, if possible, or should I say local control rather than surgery, and adjunctive medical therapy in the nastiest one.

So, as I've said, then surgery typically gets you a good prognosis in most, but you do need adequate surgical margins. So the client will need to understand, you need to remove a much bigger amount of tissue than they might originally believe. That's because you need a large amount of healthy tissue to get these roots of the tumour.

And surgery has a few limitations, . Because a lot of mast cell tumours turn up in awkward locations of the body, and there may not be enough tissue around them to take the adequate margins. You can cause degranulation when you take out a mast cell tumour and that can slow down the wound healing or cause dehissance.

And you may not be able to repeat surgery or not as easily. Once you've operated on a tumour. You will break down the protective fascial barriers that seek to contain the tumour.

And also once you've operated, you'll lay down a load of scar tissue, which will make the tissue much harder to work with on a second occasion. So the first surgery really is the best chance to cure these things. Before surgery, of course, you need to take into account the whole patient and comorbidities, issues breathing, for example, if they're brachycephalic.

You need to be able to consider how the patient will adapt to problems with the wound. If you've got a very nervous dog that needs sedation for bandage changes, should it break down, etc. Is the owner unable to bring the dog in for bandage changes if needed, or unable to afford that?

And this all centres around the issue of the margins, you know, is if you get the adequate margins, is that likely? If you get incomplete margins, are we able to do any form of adjunctive therapy? So this issue with the margins then.

It's very important. And the gold standard recommendations are 2 to 3 centimetres. Around the mast cell tumour and one fascial plane deep.

And this is based on systematic review of margins among others that was published quite recently. If you take tumours out with 2 to 3 centimetre margins, you will completely remove the majority of them, but not all, sadly. The other approach to margins is a bit riskier, and that's called proportional margins.

It's where you take lateral margins of the same length of the maximum tumour diameter. So it can be a useful technique for tumours that are very small, in very awkward anatomic locations where you just can't get the 2 centimetres. And importantly, tumours that are low risk.

Just low risk of metastasis also means low risk of tumour recurrence. So if you're going to try proportional margins, you, you'd be best advised to biopsy them before surgery. The, if you have a low risk mast cell tumour that is small, it is in an awkward location, then it may be an appropriate treatment.

But if you've got a high risk mast cell tumour, the chances are proportional margins will be inadequate and it will almost certainly recur. So when, if you get an incompletely excised mast cell tumour, you, you need to take it quite seriously. Now, failure to control local disease can be an important cause of death in mast cell tumours.

If the tumour keeps coming back and ulcerating and bothering the dog, the owner may think that he or she has no quality of life. And as we've said, surgery will be harder on the 2nd occasion. So if you get an incomplete excision, I would consider 4 things in this order.

The best one would be a revision surgery of the scar. That's where you treat the whole surgical scar as a mast cell tumour. And you take 2 to 3 centimetre margins around the whole scar and one fascial plane deep.

This may involve reconstructive skin flaps and things, but it will be the best treatment possible. Second best treatment is radiation therapy. To mop up the microscopic traces of cancer remaining.

And chemotherapy would be second to radiation. The idea is that radiation will focus its efforts on one bit of the body, whereas chemo will treat the whole body, and so it's effect is diluted, if you like. Now, some mast cell tumours, usually the low risk ones, often low grade patnick tumours, will not recur if incompletely excised.

So in certain circumstances, you could go for an active monitoring approach, but it is risky, and the owner would need to be aware that if the tumour starts to regrow again, the chances of a second surgery being effective are even less than the first. And for tumours where complete excision is just not possible, it's, it's the same hierarchy of things, really. I would go for a deliberately incomplete surgical resection, a debulk, and follow it with radiation.

And second to that, chemo. The options 3 or 4 would be radiation as the primary treatment or medical therapy as the primary treatment. Now I think that surgical debulk in the tumour will always make them more sensitive to radiation or chemotherapy, because these things will, or the efficacy of these things depends on the proportion of cells that are actively cycling.

And the proportion of cells that are cycling is inversely related to the bulk of the tumour. So if you debulk a tumour, you'll make it more sensitive to radiation and more sensitive to drugs. Now radiation therapy is an important and useful treatment for mast cell tumours.

It can be used after surgery, adjuvant treatment. After a incomplete excision to mop up the microscopic traces of mast cell tumour remaining. It can be used neoadjuvant before surgery to try to shrink a tumour down to make it more amenable surgery.

Or for some tumours that can't be resected, it could be used as a first line therapy. And in the UK at least, the adjuvant use of radiation is the most common, and it can be very effective for that. Radiation is typically given as a course of treatments, often, you know, 1520 doses, several doses each week for several weeks on the trot.

OK. It's also a dedicated centres that may be at some distance from where your practise is and where the owner lives. And because of the travelling and the repeated use of radiation, it can get quite expensive.

Radiation is often really well tolerated, but you often get acute effects, acute damage and soreness of the tissue. That typically comes on around the middle of the radiation course and resolves fairly quickly with supportive care after the radiation's finished. And on rare occasions you can get delayed adverse effects.

And the delayed adverse effects are due to killing tissue stem cells in the radiated area. These tend to come on at least 6 months after the treatments and often more than 12 months. For example, in a bit of bone that has delayed effects, you may see necrosis of the bone, and they can be quite debilitating.

But they are fortunately quite rare. So radiation is a good treatment, and particularly I like to offer it if you've got an incompletely resected tumour and a second surgery is not possible. But remember, it's a local therapy to to achieve or consolidate good local tumour control.

Medical treatment for our cell tumour is a systemic therapy. And so ideally I'd prefer to use this where you need systemic control of the disease, that is the metastatic cases or cases with a high risk of metastasis. Now, certainly, in the real world, we have to bend these principles to suit the patient and the client.

So you can certainly use it for the control of an unresected tumour, but it's often a palliative thing there. You can also use it as a neoadjuvant to shrink a tumour before surgery. And I'll talk more about that in a second.

With all medical therapy though, which includes cytotoxic drugs and the tyrosine kinase inhibitors, you need to be aware of the potential toxicities and everything could cause gastrointestinal upsets. Everything could also cause myelosuppression. Some drugs have drug specific side effects, and particularly using Lomustine, it can have a very unpredictable and potentially lethal hepatotoxicity.

The tyrosine kinase inhibitors can have lots of weird and wonderful specific effects, but commonly you can see nephropathies or hepatopathies with these drugs, which can be severe if not addressed. With the use of all these drugs, including the TKIs and including the steroids, you've got important health and safety risks for both the staff handling them or the owners handling them. And in the management of the dog's waste and the dog's body fluids.

And of course in the cytotoxic drugs, they're off licence. Some people say this tumour can't be removed, I'd prefer to treat it with chemotherapy. And this table.

Should summarise why my response is, let's try to treat it with surgery if at all possible. This is a proportion of the tumours that will shrink when the cytotoxic drugs are given, OK? Lomustine is a sole agent, more than half of them don't respond.

Prednisolone as a sole agents, 80% don't respond. And in fact, there's only two of these combinations that involve blasting and lousine, where it's creeping over 50%. OK?

The other thing that's not shown here is that all these responses tend to be finite. So you'll get the tumour to shrink down for a bit, but then it'll start to grow again. So this use of the chemotherapies and steroids in a, where a tumour hasn't been removed, tends to provide palliative effect only and in a lot of cases, it doesn't work.

Now remember what I just said that the effect of chemo is greater, in proportion to the bulk of cancer becoming smaller. So where you've got incomplete excisions, just microscopic traces of cancer, or where you've got a complete excision but with a high risk of metastasis, these things are much more likely to be successful. And indeed survival times of high risk intermediate grade mast cell tumours treated with blastine and prednisolone, for example, are are often running in several years.

And if you've got a genuine high grade mast cell tumour treated with blastine and prednisolone, it wouldn't be unreasonable to expect survival of 10 to 12 months, whereas it might be just a few months if you don't do anything. So these things are much better at working with microscopic disease, and much less able to control an unresected or amar cell tumour or that is a tumour that hasn't had any local therapy. People often talk about using steroids for mast cell tumours, and you're not wrong.

Steroids can be helpful, but I think they're best used to reduce inflammation or edoema around a mast cell tumour. As we said, the anti-mast cell tumour effect is in the order of 20%. So mast cell tumours are much less responsive to steroids than lymphoma is, for example.

There's also considerable interest in using steroids as a neoadjuvant to shrink a tumour down before surgery. And I think there is sometimes a need for this, so I would support it on occasions. But I wouldn't want to use it too much, because actually you have a much higher risk of tumour recurrence because of this.

Think that the nastiest mast cells in a mast cell tumour, that is the mast cells that are better able to adapt and survive chemo drugs. These are the cells that are most likely to be at the greater distance from the centre of the tumour. OK?

The centre of the tumour is hypoxic and depleting nutrients, so the nastiest cells will have learnt how to move away from that. So when you give steroids, you tend to pick off the lower hanging fruits. You kill the easy to kill mast cells in the centre, and the nastier mast cells at the periphery may survive.

And if you do a smaller resection, you'll probably leave the nastier cells intact, and the recurrence will be from the progeny of these nastier cells. So steroid pre-treatment, I wouldn't dismiss it completely. It can be really useful in making a tumour less vascular and less bleeding in surgery.

But it does have a higher risk of tumour recurrence if you don't do the same size excision that you were planning to do originally. Now let's review TKIs very briefly, and I'm gonna start with the tyrosine kinase receptors. Now these are very important signalling receptors found on all types of cells.

And you'll remember at the start of the presentation that the precursor of the mast cell differentiates into the proper adult mast cell under the action of stem cell factor in the tissues. So the stem cell factor like this yellow thing here, will bind these black receptors you've got here. Receptors dimerize and that catalyse, catalyses the downstream course of events that kicks off cell division, cell proliferation.

OK, among other things. Now, in around 1/3 of mast cell tumours, possibly more, you have a mutation in this receptor, such that it keeps firing without any stem cell factor binding to it. And what's more, it can't be stopped very easily.

So you get mast cell tumours told to divide all the time and to proliferate all the time with no obvious ligand. And this is the mechanism that drives the malignancy. So with the thyrosine kinase inhibitors, what we're doing is blocking.

Blocking the action of these receptors, blocking the downstream signalling, and you're effectively turning the mast cell tumour into normal mast cells again. So it's a really, really clever idea. If we look at the licencing, well, actually they're licenced for non-resectable tumours.

Even though they're systemic drugs that have an important role in combating systemic disease, it's much easier to get a response rate for them and prove they work in tumours that haven't been surgically removed, because you can measure them. And in the case of Taserinib, we find that when it's used in mast cell tumours in general, about 43% shrink. It's not much, is it?

And they shrink for around 6 to 7 weeks. Now, if you've got the CCIP mutation, however, a much greater proportion will respond. With my sit in here began around half of them respond.

And they didn't look at the response the response rates so much here, but if the CI mutation is present, you find that they stay responded for much longer. But the key point with all these TKIs is the response is finite, and it can be as low as about 3 months or as high as about 20 months. The other thing, because they're not killing cells, you need to keep giving them.

OK, they just turn the mast cell tumour into normal mast cells, so that's what they aim to do. And you need to keep giving them to sustain that effect. If you take off the TKIs, the risk is that the tumour will recur.

They've also got important toxic effects too, as well as the effects of chemo and gastrointestinal, myelosuppression, then cause hepatopathies, protein losing nephropathy, proteinuria epistaxis, muscle cramping, immune-mediated hemolytic anaemia, vascular leak syndrome, and the risk goes on and on. So they're not a panacea by any means, and they can be considerably expensive, particularly if you're keeping on using these things over months. But in some dogs, and I will stress this is the minority of dogs, you can get excellent responses.

And this is actually a colonic mt cell tumour that's causing the rectum to prolapse. And it went back to normal very quickly. And it stayed like that and it's still like that actually 14 months later.

And this is a horrible metastatic Mar cell tumour. I mean, this dog weighed 15 kg, and this tumour was the size of a grapefruit, to put it into proportion. There were numerous tumours inside the body, inside the thorax, and the liver was effaced with ma cell disease.

But again, this withered down to nothing, just with meitinib like that, and it's still in response. So a very, very small proportion of dogs have a fantastic response to these drugs. And we say that these mast cell tumours are mutation addicted.

That is, they tend to be driven by just the mutation in kit. In a lot of cancers, there's a number of mutations going on, and there's a lot of pathways that will drive the malignancy, and so just inhibiting one doesn't have such a good effect. And that's why in a lot of cases, the response to TKI drugs is disappointing.

So to sum up, because this is a, a source of a lot of confusion sometimes and quite understandably, when would I use a TKI drug or when would I use a cytotoxic drug? Well, if you've got microscopic disease, either high risk emits, or an incomplete excision. I would probably use a course of cytotoxic chemotherapy.

And I'd probably go for immblastine because it's toxicity profile is much better than Lomastine. OK? And I do this because cytotoxic drugs kill cells and progressively bash the cancer burden down and so they can be used as a course, and then stopped.

Remember that TKI drugs are not licenced for use like this. They're not as well evaluated because it's much harder to evaluate them like this. They could be expensive and there's nothing to measure their efficacy.

So if you employ a TK TKI drug at this point, you'll need to just keep giving it and keep giving it with the associated expense. If you've got a tumour that can't be removed and has metastasis or a high risk of MTS, I'd probably try TKI's first line and see what happens. And in the minority of cases, you can get an excellent response.

That's because you can measure the response. If you see the tumour shrink down, you know that the continued expense of more and more drugs and the continued risk of side effects is justified. So in summary then, mast cell tumours are common, variable in appearance, and the diagnosis is simple.

The approach to the Marcel tumour should depend on the amenability to surgical excision and the anticipated risk of metastasis. Please use clinical information as well as histopath to assess this metastatic risk. If you're staging these mast cell tumours, please don't X-ray the chest unless you're looking for enlarged lymph nodes.

You should be root. And bear in mind that may be difficult to find and routine cytology of liver and the spleen. When you treat mat cell tumours, remember that local control, which, at the moment and up till now has been provided with surgery plus minus radiation, and that's the traditional treatment of choice, which will cure over 80% of mast cell tumours.

However, it can be challenging. A medical therapy, ideally is best suited to the mast cell tumours that are metastatic or have a high metastatic risk. But certainly there's occasions where you could use it for control of a a non-resected mast cell tumour too.

And finally, to leave you with a taster of what's to follow tomorrow. This lecture has been generously supported by Verbba. That's because they brought out a unique new drug called steelfonte.

Unique. This is an intralesional treatment for mast cell tumours. That promises to be have a skin sparing effect, so you don't need to take margins, but yet can cause complete response of the mast cell tumours.

So it could be very useful for the mast cell tumours at low risk of metastasis and in very awkward locations of the body. And that's where I'm most interested in seeing how this drug turns out. The licencing is for the treatment of non-resectable, non-metastatic subcut mast cell tumours located at or distal to the elbow or the hock.

And non non resectable, non-metastatic, cutaneous mast cell tumours in any location in dogs. Now the tumours need to be relatively small, up to 8 cubic centimetres in volume, and must be accessible to intra-tumoral injection. So I'm very excited to see how this thing will turn out, and I'm looking forward to using it in my practise.

If you're wondering how it works, then tomorrow, Doctor Pam Jones is going to tell us much more about it. But it has a direct oncolytic effect mediated through protein kinase activation. It causes inflammation and necrosis of the tumour tissue resulting in local tumour destruction that I understand is targeted pretty much to the tumour only and spares the surroundings.

So thank you ever so much for listening. And if you've got any questions, I'll try to take them now. Thank you.

Owen, thank you very much, and what a fantastic teaser to tomorrow night's part two. So, thanks, Owen, and a huge, huge big thank you to Verbe for their sponsorship. As Owen alluded to, very generous sponsorship both tonight and tomorrow night.

So, same place, same time tomorrow. And then you can hear about this new fantastic treatment from, Pamela Jones. Owen, that was absolutely fascinating and you made it sound so simple, but you have really stirred the hornet's nest, with your taking biopsies of the mast cell tumours.

Lots and lots of questions surrounding it. So I'm just gonna paraphrase, but basically, the questions were, are you not risking the animal's life? Should you be pre-meding with antihistamines?

And are you not going to encourage metastasis? So, to biopsy a mast cell tumour, I probably would use antihistamines if I'm gonna cut into the centre of the tumour. That's because you're with the best will in the world, going to promote degranulation to some degree.

So, for an incisional biopsy, I would give an H1 blocker, like chlofeurramine, and also an H2 blocker like ranitidine or famotidine. And I would make sure that the biopsy wound is well sutured because the local degranulation, as we said, could impair wound healing. However, biopsy of the mast cell tumour should not encourage metastasis, and it should not be a life threatening procedure by any means.

The worst you're going to do by biopsying a tumour is make it bleeding and have a messy wound that takes longer to heal. So you can plan against that by very carefully taking the biopsy and suturing it appropriately. OK.

How long before, the surgery would you start your H1 and H2 blockers? Would it just be a pre-med or would you start it a few days before? No, I would use it as a pre-med.

OK. And carry it on afterwards? I might give it for one day or so, but not a long time afterwards, no.

The degranulation, if it's gonna happen, is quite acute. And, and as you saying in the beginning. Yes, sure, yeah.

Just quickly before we go on with other questions, I just want to point out, folks, we cannot discuss individual cases tonight. So those of you, Judith and the others that are writing in about your cases and everything else, we can't discuss those on this forum tonight. I'm really sorry about that.

Oh, and Ruth wants to know approximately what is the cost of sentinel lymph node mapping. That my practise, that is not something we offer as an outpatient procedure. It's for cases that we see as a full referral.

And that's because after we've mapped the sentinel lymph nodes, we will then try to FNA it. And we may also FNA other things under ultrasound guidance, and that requires a vet on the ground next to the dog, making clinical decisions about what we should and shouldn't do. So my practise and, and I feel that it's not appropriate to do that as a pick and choose outpatient procedure.

But for dogs who I see for mast cell tumour staging, during the consult, bloods, general anaesthesia, CT scan, including sentinel lymph node mapping, aspiration of sentinel lymph node, liver and spleen, costs in the order of about 1800 to 2200 pounds, depending on the size of the dog and various specifics. OK, fantastic. Thank you.

I think you've covered this quite extensively, but we have a lot of questions coming through about the benefits of either pre-surgical chemo or pre-surgical radiation. Can you just give us a quick synopsis of those again, please? Yes, of course, and it's a, it's a tricky area.

But basically, in, if the tumour is absolutely non-resectable, then I think there is a place for using pre-surgical chemo or radiation to cytoreduce it. It's really not a perfect thing to do though, because cancers are very heterogeneous, and there is a process of natural selection and survival of the fittest going on within every tumour. The centre of the tumour is very hypoxic and it's nutrient deplete.

So that applies a selection pressure for those tumours that are better those cells that are better able to survive in harsh conditions. And their means of survival is often motility to go to other parts of the body or move away from the edge of the tumour. And the same means of survival involve inducing genes and transcription factors that will protect the cell from all kinds of other things like drugs or like radiation.

So, to put it very simply, you'll, the cells in a mast cell tumour at the edge are very different from the ones in the centre. The ones at the edge are the most evolved and resistant cells. And if you've got a large tumour, you will kill a lot of the easily killable mast cells in the centre with steroids or chemo or radiation.

But you're never gonna kill every single mast cell, it just won't work like that, I'm afraid. And the ones that are most likely to survive will be the most peripheral. So if you then do a resection and resect what you can see or slightly smaller than what you thought you could see, you're likely to leave the most peripheral, in other words, the most tough mast cells behind.

And then when the tumour recurs, it will be from these extra tough mast cells. So in theory, if you have reduced the size of a mast cell tumour with chemo or radiation, You should be doing the same level of resection that you would do initially. OK.

Well, you've just answered Jose's next question. So that's fantastic. There you go, Jose.

Keep your margins to what the original tumour size was. Owen, we've got another question coming from Caroline and it says, would you consider the use of electro chemotherapy for incomplete excision of mal tumours? Yeah, there, there have been some studies with the use of electrochemotherapy.

The, I don't think there's been enough of them to say it's definitely a good thing. I think the the standard evidence we have is that radiation therapy would be the best treatment for an incomplete resected. Well, sorry, revision surgery #1, radiation #2, and then chemotherapy number 3.

There are some interesting studies, . Overall, it represents a very small number of dogs and quite a heterogeneous group of cases, but there's preliminary evidence supporting the use of electro chemotherapy. And from a pragmatic point of view, I would say if surgery, radiation or chemo are not possible, then electro chemotherapy would be something to explore.

Fantastic. Thank you. I'm not going to pronounce this next person's name.

I'm sorry, but they want to know if you have money problems with the owner, would you consider using triamcinolone to shrink and control the tumour? Yeah, you could do. I mean, there is support for doing that, and I presume the questioner means intralesional triumphs in alone.

The, I, I've tried that on a few occasions for palliative care of tumours that are causing a lot of trouble and are metastatic. For example, a very large ulcerated tumour right next to a dog's eye. And this tumour had been resected once.

It had radiation, yet it had recurred. It was also metastatic, and the dog, had failed chemotherapy to control the metastatic disease. The dog was doing OK, it was just the ulceration of the tumour was life, quality of life limiting.

So as a palliative procedure for a few weeks, we tried intralesional triamcinolone, and we got a modest response. So I don't think it's going to get you a very long or durable control of the tumour. And of course for tumours that are metastatic, it's not gonna do anything for the disease in other sites.

But it can be used palliatively, as I described. OK. I know you said at the beginning that Marcel tumours don't have any sex predilection, but Mario is asking, does neutering have any effect on Marcel tumour incidences, or, you know, specifically and with related to any breed?

No, I'm, I'm not aware that there's any influence of neutering at all. I think Marcel tumours can occur in any dog, but it's the, it's the popular breeds who seem to get the most. Just as a As a philosophical point, a lot of studies will show that neutered dogs have a greater incidence of cancer, but then neutered dogs also have a greater likelihood of being well cared for and taken to the vets when they're ill.

So you've got to be very careful with some of the data about neutering, but I'm not aware of anything supporting a greater likelihood of ma cell tumours in neutered dogs. OK. Catriona says that, when she was a new grad some 20 years ago, there was a fashion of intralesional sterile water.

Did this ever work or was it just a myth? Yeah, I don't think it worked very well. I think it's, yeah, there was a paper on it a few years ago.

I, I don't think it's a very effective treatment and it, it might have a direct cytolytic effect just by altering the osmotic balance in and around the cells. But again, that's gonna be a temporary thing. Yeah.

And of course, if you're interested in intralesional treatments, please come to Pam's Talk. It's gonna be very, very exciting. It really is.

I'm busy scrolling through what I would only as pages of fantastic accolades for you and yeah, as Anthony always likes to say, if we were in an auditorium now there would be thunderous applause for you. So there really are loads and loads of people writing in saying fantastic webinar. Thank you so much.

And it goes on and on. I don't want to give you too much of a swollen head tonight. That's, that's very kind, thank you.

I'm glad people found it useful. Ruth has come up with an interesting one and says, are mast cell tumours one of the tumours seen with Apaquel use as noted on the data sheet. That is an interesting question, isn't it?

I think, I, I think with use of anything immunosuppressive, . You can reduce the body's immune surveillance and you do predispose to the formation of cancers. And I know there's some data showing that cats given cyclosporin at a high dose before renal transplantation, had a significantly greater likelihood of developing lymphoma.

But I'm not aware of any such data in dogs actually. And the some of the new immunosuppressives licenced for control of skin disease have a contraindication on the label for any malignant cancer. I'm not aware of any specific one being a problem.

And from a first principle's point of view, I wouldn't exclude the possibility of any cancer forming in a dog who's on immunosuppressive treatment. Yeah, yeah. There's loads of questions coming through again, of stuff that we've already answered.

Folks, my advice, if we don't get to your question tonight, it's probably been answered already during the presentation. So log on to the webinar vet's website in a day or two's time when this recording will be up online and Go back and listen again because they, a lot of these questions have been answered. But Karen has got a very interesting question.

She says for FNAs, would you take the sample at the margin of the tumour to get those nasty cells, or is the grade likely to be different in the centre? So for, for an FNA, your principal question is, is this a mast cell tumour? Yes or no.

So I would take that from the most convenient place, the place where you think you can immobilise the tumour and get a good sample of it. For, if you're taking an incision or biopsy. Then that should be representative of the tumour.

So a true cut could be considered or a kind of slender wedge of tissue that might represent different areas. The Sometimes it is quite clear that the grade on an incisional biopsy is a lower grade than the one you get after you remove the tumour because you've biopsied a region of the tumour where the cells look a bit nicer and are a bit slower in their division than they could be in other areas. So, yeah, that's one of the problems with small incisional biopsies, I'm afraid, and there's no easy way around that.

There's no predictable way of saying which area of the tumour is easier to biopsy. It just has to be representative in some form, and you could look at taking a long thin biopsy that takes into account different areas of the tumour, or you could take a couple of biopsies. The only thing I would say is that if you don't know what the lesion is before you take a biopsy, please take it from the centre.

And that's because there are some lesions, and a very good example is the injection site sarcoma in cats that can be fueled by the inflammation you create when you cut into it. So if you get, I'm talking cats with injection site sarcomas now, not mast cell tumours, but it's an important point. If you're biopsying a cat with a lump between the scapula, and you do it off to the side, you will have the cancer walking down that biopsy tract by the time you're taking stitches out.

So if you don't know what the lump is, please go from the centre. Otherwise, just try to make sure it's representative as best as you can. Fantastic.

Owen, thank you so much. I'm, I cannot tell you, I'm scrolling through pages and pages of fantastic comments and just so many accolades and thanks to you, Owen, for your time and for sharing tonight. I think that's about all the questions that we've got that you haven't answered again.

As I say, there's a load of questions there that you have answered and I'm not going to, to ask you to repeat yourself again because we are recording and this recording will be up online. So if we haven't answered your question, if it wasn't a personal case that you're on about, go back, go online. I promise you everything that I've seen there, Owen has already answered.

Owen, thank you for your time tonight. We really, really appreciate it. And thank you for wetting our appetite for Pam's presentation tomorrow.

OK, thank you. Thank you to everyone.