So good evening everybody, and thank you for tuning in this evening. So I would like to introduce Aaron Harper, who's our presenter for this evening. So after graduating from the University of Cambridge in 2008, Aaron spent 5 years in general practise.

In 2016, he completed a residency in small animal oncology, and during this residency time, he completed the certificate in advanced veterinary practise in small animal medicine. He passed the European diploma in Veterinary Internal Medicine and oncology in 2017 and then became a European and Royal College of Veterinary Surgeons recognised specialist in oncology. Aaron's main areas of interest are haematological cancers and the medical management of these conditions.

He's also interested in novel therapies for dogs and cats with cancer and the management of side effects in these cases. And his research to date has been on this subject. From these interests, he has further developed a particular interest in treating feline lymphoma.

And tonight, Aaron is discussing feline lymphoma, the presentation, diagnosis and staging. So over to you, Aaron. Thank you very much.

Thank you for the introduction and thank you everybody for coming to listen to me this evening. I am, as Caroline said, going to talk about the presentation, diagnosis, and staging of feline lymphoma. I'm not really gonna focus on the treatment, but there's a bit of a shameless plug right at the start, and that if anybody's interested, my colleague Sarah is gonna talk about treatment of feline lymphoma in a couple of weeks' time.

So the aim for this evening is that we're gonna talk, initially about the presentation, of feline lymphoma, then move on to a little bit on, looking at how we can diagnose the, the disease, and then look at the usefulness of staging in cats with lymphoma. So the first thing to say is that lymphoma is a cancer that arises from a clonal expansion of lymphocytes, and it is the most common commonly diagnosed cancer in the cat. However, feline lymphoma actually represents a group of diseases, each of which have their own aetiology, progression and prognosis.

Although we're all used to the adage that cats are not small dogs, this is particularly true for feline lymphoma. There are many peculiarities that are unique to cats, both in the diagnosis and the treatment of the disease. Due to the heterogeneity of the diseases that fall under the feline lymphoma umbrella, the, the literature can be quite confusing and sometimes even contradictory.

The problem is that many of the different subtypes of lymphoma are often grouped together, in the same research paper looking at, treatment and prognosis. And that can make looking at, trying to get form evidence-based decisions from that literature, is quite difficult. We know that lymphoma is common in cats, and in fact it makes up to up to 25% of all the feline malignant tumours.

And we'll go through a few of the different types of feline lymphoma, and you'll see that the age of presentation varies with the anatomical site. So we'll start by looking at a little bit of aetiology. And the cat is interesting in that we actually do have recognised etiological factors, that cause lymphoma, which is quite different to dogs, for example, where, a lot of the time we just don't know, why the lymphoma has arisen.

So in cats we can identify viral causes, immunosuppression, environmental causes, and also the role of chronic inflammation and potentially causing lymphoma. So viral cause of lymphoma are well recognised in the cat and it's specifically the retroviruses such as the feline leukaemia virus or FERV and the feline immunodeficiency virus or FIV. So in the past, one of the main causes of lymphoma was infection with the feline leukaemia retrovirus.

And around about 20 years ago, nearly 20% of the lymphomas in cats were thought to be caused by FERV infection. The typically affected cats were young and often presented with the extranodal forms of the disease, such as spinal, ocular or mediastinal forms. Now you can see that as vaccination became prevalent through the later 80s and the 90s, the incidence of FERV dropped in the feline population.

One of the interesting things that this caused was actually a change in the age distribution of feline lymphoma. So we saw a shift away from young FERV positive cats towards old FERV negative cats. Now cats do not necessarily have to be persistently infected with FERV to be at risk of the of lymphoma.

Individuals that have been exposed to the virus but are zero negative can have the pro virus incorporated into their DNA and they're at an increased risk of developing lymphoma, anywhere between a 5 to up to a 40% risk depending on the, the publications that you read. However, we know that cats that are persistently infected with the virus and that are that are sero positive have a much higher risk of developing lymphoma, so up to 60 times compared to an FVRV negative cat. The role of FIV in, causing lymphoma is thought to be less important, and cats have a relatively modest 5 times increased risk of, lymphoma of developing lymphoma if they're positive for FIV.

However, if you combine the two, so FERV together with FIV, increases the cat's chance of developing lymphoma up to 80-fold. FIV is also a cause of general immunosuppression in the cat. And immunosuppression, we know it is another factor that can, increase the risk of developing, feline lymphoma.

Another cause of immunosuppression is using, immunosuppressive medications such as cyclosporin. And two studies relatively recently in the United States that have shown that cats that receive cyclosporin following kidney transplantation are up to 6 times more likely to develop lymphoma. This phenomenon is known as post-transplant lymphoroliferative disorder in man.

And it raises the concern of the increasing number of cats that we have, in the UK that although they may not be receiving immunosuppressive medication post-transplantation, there are many cats receiving cyclosporin for, chronic skin disease or, immune-mediated, hemopoietic disease such as IMHA. Some of the other factors, in terms of causing lymphoma in cats are less well understood. I mentioned, environmental factors, and there was one study that showed that exposure to environmental tobacco smoke in cats increases their risk of developing lymphoma around about threefold compared to cats that aren't exposed to tobacco smoke.

The other final thing that I mentioned briefly was the role of chronic inflammation. Now there are increasing numbers of specialists who believe that there is a link between chronic inflammation and lymphoma development in cats. Particularly cats that may have had chronic rhinitis or inflammatory bowel disease that go on to develop lymphoma in those organs.

Although trying to prove this is very difficult, as, as you can imagine, we need a long term cohort, study, to follow cats almost over the period of their entire lives. And so far, the evidence, base to back this up is lacking. So the next question is how do we classify lymphoma in cats?

And the typical way is to look at the anatomical site that's affected, the grade of the lymphoma, so whether it's low or high grade, and the phenotype. So often the size of the neoplastic lymphocyte is substituted for the grade. So you'll see small cell and low grade are used interchangeably.

And similarly, large cell is used as a synonym for high grade, where both terms are used to describe biologically aggressive disease. So, if we, extrapolate that, one of the most common forms of lymphoma in dogs and in man is diffuse, so the anatomic sites basically everywhere. Large cell or high grade, B cell lymphoma, or DLBCL to make that short.

In cats, however, the phenotype has not really been shown to be prognostic in a variety of studies, and it's often not used in the description of feline lymphoma. It's therefore typical just to use the anatomical site and the grade. So for example, we might say high grade multicentric lymphoma or small cell intestinal lymphoma.

Lymphoma can arise anywhere in the body, and it's often classified as either nodal, which means it's arisen from a focus of lymphoid tissue, or extranodal. Alimentary lymphoma is the most common form of lymphoma in the cat, and it's often considered as a nodal form of the disease because it arises from the mucosa associated lymphoid tissue of the intestine. Medtinal lymphoma is also considered to be a nodal form of the disease.

However, extranodal lymphoma is also common in the cat and includes the skin, nose, kidneys, central nervous system, larynx and trachea. The list is endless. The cat can basically develop lymphoma anywhere in the body.

So we're gonna go on and talk about some of the specific anatomical sites of lymphoma now and this slide just lists those sites that we're gonna go through. So we're gonna start with nodal lymphoma in cats. And so, by this I mean lymphoma that actually affects the lymph nodes.

This is probably the most common form of lymphoma that we're all aware of, in dogs that present with multicentric lymphoma, with lots of enlarged peripheral lymph nodes. So it's common in dogs and in man. However, cats, because they like to be different, it is very rare.

So actually only around about 4 to 10% of all lymphoma cases in cats comprise nodal lymphoma. Cats, quite often have regional lymphadenopathy, and that's more common than the multicentric, form of the disease, and. We have to remember that a peripheral lymphadenopathy in a cat should be distinguished from non neoplastic diseases such as the syndrome of idiopathic lymphadenomegaly of young cats, and also various infectious diseases such as Bartonella, mycobacterium, toxoplasma, the retroviruses, feline infectious peritonitis.

So there is a variant of nodal lymphoma that occurs, in the cat, which is known as Hodgkin's-like lymphoma. So in man, Hodgkin's lymphoma is well described, and it is a disease that affects, local regional lymph nodes. So usually in the neck and the upper thorax.

It has slow onset and progression, and a classic appearance on histology. And there's a picture here of the classic appearance that you see. This type of lymphoma has only been reported in the literature in a relatively limited number of cats, although it is a well recognised disease entity.

The confusing thing is that the disease has also been referred to as T cell rich B cell lymphoma due to the immunohistochemical staining of the lymph cyte populations. However, the nomenclature is a little bit confusing, and there is some contradiction in the literature, as some people, report, well, say that T cell rich B cell lymphoma is a distinct syndrome in man from Hodgkin's like lymphoma, and therefore we shouldn't use these terms interchangeably in the cat. The treatment protocols in cats have not been well established, and even with just local therapy, extended survivals have been reported.

And we definitely need some further research into this subtype of lymphoma in cats, so that we can establish more defined treatment protocols. So moving on to alimentary lymphoma, this is definitely the most common form of feline lymphoma. The median age of diagnosis is around 12 years, and all breeds of cats seem to be similarly affected.

There are two distinct types of alimentary lymphoma in the cats that have very different presenting signs, progression and prognosis. And there have been several different attempts at trying to classify these diseases, which again unfortunately has led to some confusion in the nomenclature. The easiest way and the most useful way to distinguish penis diseases is to think of them as either high grade or low grade intestinal lymphoma.

The majority of these lymphomas are T cell lymphoma, certainly the ones that affect the small intestine. B cell lymphoma in the cat's gut is rare and it typically affects either the stomach or the large bowel. So a high grade intestinal lymphoma is akin to the form of lymphoma in man called enteropathy associated to T cell lymphoma or EATCL and it's akin to the type 1 disease in people.

Affected cats will have moderate to severe gastrointestinal signs and weight loss over a moderately short period of time. So the high grade disease equals a, quite rapid and aggressive progression. On histology, the, neoplastic lymphocytes efface the mucosa and the submucosa, and often a transmural as well.

And it's quite common to see affected cats will have involvement of other abdominal sites, including the lymph nodes, liver and spleen, sometimes even organs such as the pancreas. Often an abdominal mass can be pal palpable due to either a lymphomatous mass in the intestine or an enlarged mesentoic lymph node. And sometimes we see cats have such widespread abdominal disease that it is impossible to identify the organ of origin.

And these cats are just simply diagnosed with abdominal lymphoma. The prognosis of this condition is guarded, although some recent literature contradicts historical publications regarding their survival. So EATCL type 2, lymphoma is kind of the opposite side of the coin to type 1.

So this is what we would consider to be either small cell or low grade. Again, the terms are interchangeable. This form of lymphoma, in the cat gut represents maybe 50 to 80% of the disease, and it is much more indolent in its nature.

So cats can have mild clinical signs for several months. And in terms of presentation, it's often impossible to distinguish low grade lymphoma from inflammatory bowel disease. The disease is often associated with the mucosal associated lymphoid tissue and remains mucosal often with significant evidence of epitheliotropism.

The diagnosis of the disease, specifically trying to differentiate it from an inflammatory bowel disease can be challenging and probably requires a multi-step approach, which I'm gonna come back to later. The prognosis is relatively good, and there is prolonged survival reported with low intensity chemotherapy. Now to talk a little bit about mediastinal lymphoma.

So historically, media sinal lymphoma was common. The affected cats were young and they were FELV positive, and they had a very poor prognosis. However, since the introduction of the FELV vaccine, the incidence of mediastinal lymphoma overall has reduced.

The most common presentation now still seems to be in young cats with a median age of 3 years old. But Siamese cats, and particularly male Siamese cats seem to be very predisposed. They often present with acute signs of respiratory distress due to a large mediastinal mass, potentially together with the effusion, as the cat in the major graphs, has.

But the prognosis, for the FERV negative form can be good, with a reported survival of over a year with chemotherapy. So, I'm gonna go on now to talk a little bit about some of the extranodal forms of lymphoma. What I wanted to say at this stage, though, was that a lymphoma should be a differential for any sick cat that walks in through the clinic door.

The clinical signs are quite often dependent on the body system affected. However, they often do the sick cat typical thing of having just lethargy, weight loss, and anorexia. And they're quite often presented quite late in the disease course again because of the vague clinical signs.

So now looking at, nasal lymphoma, this is the most common form of extranodal, lymphoma in the cat, and it is actually the most common nasal tumour in the cat as well. The median age of presentation is around 9 years, although there is a large age range of cats, you know, 3, being reported to be affected. And clinical signs are usually those associated with the upper respiratory tract that stir to sneezing and nasal discharge.

Again, some cats seem to have had chronic rhinitis for years before going on to develop lymphoma. Up to 20% of patients can have local extension and or potentially systemic involvement as well. And therefore careful staging is required if local treatment is planned, which again I'll come back to you later.

The majority of nasal lymphomas are B cell in origin, although immuno phenotyping is only performed if the diagnosis is not obvious on histology alone. They are also usually high grade tumours. They can have a good response to er therapy, either chemotherapy or radiotherapy, and the prognosis can be very good, even if the cats seem to have a large burden of disease, as the cat on the CT image has.

Renal lymphoma is the second most common form of extranadal lymphoma in the cat. The median age of presentation, is 9 years, but again, it can affect very young cats. The clinical signs are often vague, including lethargy and weight loss.

Although if significant renal compromise occurs, then owners may notice, polyuria and polydipsia. Quite often on abdominal patient and irregular firm, enlarged kidney, it is often detected. And extension to the central nervous system may occur in up to 50% of cases.

The prognosis is guarded, although good outcomes can be achieved in cats with multi-agent chemotherapy. Then, a little bit about CNS lymphoma. It is one of the most common CNS tumours in cats.

Up to 30% of brain and spinal cord tumours are lymphoma. And the disease can be primary or part of the systemic process. The presentation is very variable and caps may present with seizures, obtundation or altered behaviour.

Pain is the most common presentation of captive spinal lymphoma. And in the brain, on advanced imaging, the lymphoma can manifest as a sultry mass as lymphoma to cerebri, which might be difficult to differentiate from an inflammatory condition, or intravascular lymphoma, where the disease is located around the, vasculature in the brain. The prognosis is very guarded and chemotherapy might not be successful due to the poor penetration of the blood-brain barrier.

OK, so we've talked a little bit about presentation of phenline lymphoma and the different ways that lymphoma can affect the cat, and we're now gonna move on to a little bit about diagnosis. So, a baseline should be obtained in any cat suspected of having lymphoma, which consists of haematology, biochemistry, and urinalysis. Although these are actually rarely diagnostic for the lymphoma, these tests help to exclude other possible differential diagnosis, and also, they help to establish the basic health status of the patient.

Cats with intestinal lymphoma can have liver involvement, which could cause raised elevation of liver enzymes. And similarly, cats with renal lymphoma may be azotemic, although the degree of azotemia does not correlate with the burden of disease, and a lack of azotemia does not actually exclude renal lymphoma as a differential. Baseline testing is also important, as many cats of lymphoma are middle-aged and may have other concurrent diseases such as chronic kidney disease, which is an important consideration for chemotherapy.

Retroviral testing is also important in any cats suspected of having a lymphoma. Also, any middle aged or older cat that are presented with weight loss should have a basic thyroid panel performed and assessment of intestinal absorption function certainly with carbalamine. A significant number of cats with intestinal lymphoma will also be hypocaminemic and may require supplementation.

In general, cats often present with a mild anaemia and the cause can be multifactorial. The most common cause of anaemia would be a anaemia of chronic or inflammatory disease, in which case it will be non-regenerative. Other possible causes could include a blood loss anaemia due to a bleeding lymphomatous mass, for example in the small intestine, or a perineoplastic immune-mediated hemolytic anaemia.

It is relatively rare to get bone marrow involvement of lymphoma in cats, but that could also be another potential cause of anaemia, in which case we'd expect to see other cytopenias as well. It is also common to see changes to the serum proteins with a lower albumin and a high globulins indicative of an inflammatory response. Cats with lymphoma may also have a protein losing enteropathy, in which case they can present with severe hypoalb anaemia, and potentially ascites as a consequence.

So, although it seems a little bit obvious to say, the choice of imaging for a suspected phenile lymphoma does depend on the body system that is affected. In most cases, thoracic radiography and abdominal ultrasound are sufficient to identify abnormal lesions. It should be noted, however, that ultrasonic ultrasonographic appearance alone is not sufficient to diagnose lymphoma, and biopsy sample should always be performed, which I will come on to in a second.

Several studies have shown a poor correlation between ultrasound appearance and histopathological diagnosis, particularly in diagnosing, round cell tumours such as lymphoma. A very recent paper has just shown that the honeycomb spleen appearance of a cat on ultrasound, which we, quite often have presumed to be a lymphoma in the past, actually correlates poorly with the diagnosis of neoplasia. For nasal lymphoma, CT may be required to assess the extent of the disease, however, good quality radiographs can often raise the suspicion of an intrained nasal mass and many cats can be diagnosed with radiographs and a biopsy.

For investigation of intracranial disease or spinal disease, an MRI and CSF tap is probably gonna be required. So we're gonna move on now a little bit to look at some biopsy techniques in trying to establish a diagnosis of lymphoma. Cytology is often considered to be the first line biopsy technique, and it's always the test that oncologists like to do first for several reasons.

The advantages are that it is easy. It is relatively cheap. It's quick to do, and we'll also get the results quickly, hopefully within 24 to 48 hours, and it is minimally invasive.

Normally when we're we're talking about dogs and diagnosis of lymphoma, we always say, oh, and you can do it conscious as well, which may not be achievable in a cat depending on how cooperative they are. For many feline high grade lymphomas, cytology can achieve the diagnosis. And this, is more likely, particularly for something like a high grade intestinal lymphoma, where you're FNAing a an enlarged mesenteric lymph node or mediastinal lymphoma when you've got a very large mediastinal lymph node.

Often they exfoliate a nice population of large atypical lymphocytes, such as the picture on the side here, and the lab will be able to give you a diagnosis. However, cytology can also be less useful, particularly for lymphomas that do not exfoliate very well, or instances where there is significant inflammation that may confound the results. So, for example, feline peripheral nodal lymphomas often have a mixed lymphocyte population and diagnosis can be quite challenging.

Hodgkin's-like lymphoma is particularly challenging, and a study has shown that cytology from these lesions is often reported as lymphoid hyperplasia rather than lymphoma. Another, issue for cytology, as I said, were, for organs where you get poor cell yield, such as the kidneys or actually the intestine intestinal wall itself, and quite often we'll get a non-diagnostic cytological biopsy. The other point, I should just mention before moving on to cytology is for the cases where you have a neoplastic pleural effusion or an abdominal effusion, quite often we can isolate, the neoplastic lymphocytes in that effusion, which is a relatively easy way to achieve the diagnosis.

The problem in the cat is that they like to, any inflammatory process often is quite lymphocytic and reactive lymphocytes can sometimes masquerade as neoplastic ones. So if you think then a little bit about histology, although it's more invasive, histology of an excisional biopsy often allows for a definitive diagnosis to be achieved. So if you have a cat with a an enlarged peripheral lymph node, then excision of the entire lymph node should be performed so that the pathologist can address the er architecture of the node.

Tissue biopsies also permit immunohistochemistry to be performed, which may aid the diagnosis, and that's particularly for cases of Hodgkin's like lymphoma. The other advantage of a excisional biopsy of a lymph node, for example for a Hodgkin's like lymphoma, where only one lymph node is affected, then removal of that node may also be therapeutic as well as diagnostic. One Point to bear in mind is if that, if there is any concern for mycobacterial disease in your patient, then it's advised to spare some of the lymph node, and freeze it straight away after collection.

So, essentially, chop the lymph node in half, send half of it to the lab where it will be fixed for histology, but keep the other half in the freezer. If the pathologist then comes back to you with a suspicion of mycobacterial disease, you have fresh frozen tissue, on which further mycobacterial testing can be performed. So for nasal lymphoma, obtaining samples can be challenging, although a variety of methods have been reported.

Nasal flush techniques are relatively straightforward, although they might not yield sufficient tissue. Alternatively, rhinoscopy or blind grab biopsies can be performed. However, the tissue samples you get are often quite small and can be non-diagnostic, especially with, endoscopically guided biopsies because of the size of the cat's nose and also the size of the biopsy channel in the endoscope.

The forceps you have to be very, very small. Biopsies for intestinal disease can be obtained either by endoscopy or exploratory laparotomy. Although endoscopic biopsies are less invasive, only mucosal samples can be obtained and may therefore not be fully representative.

For the diagnosis of high grade intestinal lymphoma, this may be sufficient. However, for differentiation between low grade lymphoma and inflammatory bowel disease, full thickness biopsies are preferential. Explorative laparotomy may therefore be a superior method to achieve diagnostic biopsies and also has the advantage of allowing other abdominal structures to be biopsied at the same time.

For high grade disease in cats that present with a solitary intestinal mass, surgery may also be therapeutic. And some studies have shown a superior survival in cats that receive surgery and chemotherapy compared with chemotherapy alone. So we're, while we're talking about histology, I'm gonna stop for a second just to have a quick chat about the grading of lymphoma in cats.

So grading is the process where the lab assigns the pathological, description of the lymphoma. There are various different grading schemes, around for lymphoma, although the one that is currently most widely used is the WHO grading scheme. Engrading of lymphoma in man and in dogs has been shown to be prognostic and will also influence the first line treatment.

And as we've already kind of briefly said, it uses the grading scheme utilises the cell size, the distribution, and the phenotype to classify the disease. Grading can only be done on histopathological samples. So the question is whether grading is useful in cats.

And this study, which was performed in 2017, or which was published in 2017, looks at trying to apply the WHO grading criteria to cats. There were only 30 cats overall, and given there are many, many subtypes of lymphoma in the WHO grading scheme, then there were, unfortunately, small numbers assigned to each histological subgroup. And this made interpretation a little bit difficult.

The most commonly diagnosed disease was peripheral T-cell lymphoma due to the high number of cats that had high grade intestinal or abdominal lymphoma. The study did confirm that cats with low grade T cell intestinal lymphoma and T cell rich B cell lymphoma had the best prognosis. And the study does reinforce the idea that it is anatomical subtype and the different differentiation between large cell and small cell, which is the most important factors in, giving us prognostic information in cats rather than the actual phenotype of the disease.

So moving on with our list of possible diagnostic tests, we're going to think a little bit now about the molecular diagnostic techniques that are available in cats. So molecular diagnostic techniques have been used to help in the diagnosis and classification of lymphoma. These techniques are commonplace in human oncology, and they have been fairly well standardised in get investigation of canine lymphoma.

The techniques have also been investigated for feline lymphoma, however, the use has not become commonplace, and there are a variety of reasons for that. The first test that we're going to talk about is the PCR for antigen receptor rearrangement or PAR. So this is a useful test to look for canality in diagnosing lymphoma.

The The technique only requires a few cells to be successful and therefore it is useful because it can be performed on virtually any sample. So, for example, it can be formed on a blood sample, it can be performed on the harvest from an FNA and whether that is already on your glass slide or not, it doesn't matter. And it can also be performed on tissue, either fresh or fixed.

It's particularly useful in situations where obtaining tissue for histology and immunohytochemistry would be challenging. So for example, those cats with abdominal lymphoma that are very sick or cats with renal lymphoma, for example. PAR is used to, essentially tell us whether the population of lymphocytes that we have harvested from our patients is neoplastic or not.

So it's quite often used to differentiate inflammatory from, neoplastic lymphyte populations. It can also be useful if your sample is very small and if the lab cannot tell just on a few lymphocytes whether that is neoplastic or not, then PA might be able to give us a little bit of extra information. However, there is a big disadvantage in cats, and that is that the reported sensitivity of the test is very variable.

So anywhere between 50 to 100%, depending on the publication that you read. And the reason for the variation is that it does seem to be very dependent on the lab and on the primers they use. So the problem is that if you have a sensitivity of 50% for the test, then false negatives might be very common.

The other molecular diagnostic test that we are just going to consider briefly is flow cytometry. So this can be used for diagnosis and finger typing of lymphoma, although in cats, the panel of commercially available antibodies is relatively limited. It should also be noted that flowsometry is only available in certain labs in the UK.

Specific sample collection is required and it's advised to contact the lab for advice before collecting samples to ensure they are appropriate. And sample cellularity is a major factor in the likelihood of a flow cytometry sample yielding usable results. So, a study did find that sample cell cellularity is significantly influenced by the needle size with 21 gauge needles providing a high cellularity.

This study also demonstrated that sample cellularity and the likelihood of being processed did not vary between peripheral and intra-abdominal lesions. Now, to send samples for flow cytometry, the cells need to be in suspension. So you can either send a blood sample if the cat has a significant lymphocytosis, or you need to contact the lab in advance for them to be, for them to send you some, transport medium to send the sample in.

And the sample must also be processed within 24 hours of being harvested. So there's no point taking your samples on a Friday and for it to arrive at the lab on the Monday. So both par and flow cytometry do have utility in confirming the diagnosis of lymphoma, but due to the problems that I said, are probably not great but to be used to stand-alone tests for the diagnosis of lymphoma in the cat.

So one particular problem in feline lymphoma, as I've already briefly mentioned, is the diagnosis of low grade intestinal lymphoma and being able to differentiate that from inflammatory bowel disease in the cat. And this is an area of ongoing er er research in a number of different groups. The problem is that cytology has been shown to be poorly diagnostic and even histology on full thickness intestinal biopsies may not be reliable.

This study, done by Sabatini and colleagues, compared cytology, histology, immunohistochemistry, and par to the diagnosis of low grade intestinal lymphoma, and correlated each test with survival, to the cohort of patients that they found. They found that using stratified the cat into two groups was a significant difference in survival. And this graph, shows the difference between, the cats that had a negative par result and therefore were diagnosed with inflammatory bowel disease compared to the cats that had a positive PA result and therefore diagnosed with lymphoma.

And that difference in stratification was most pronounced with the, with power testing. They therefore assumed that power would be the gold standard for differentiating between these two diseases. And they then compared the other methods, so cytology, histology, and immunohistochemistry, to, power analysis.

And you can see that, cytology has a very poor sensitivity and a reasonable specificity, where, the histology and even immunotochemistry still have relatively poor sensitivity, but pretty good specificity. This means that if one of these tests give you a positive diagnosis for lymphoma, then it probably can be believed, but if they give you a diagnosis, a negative diagnosis of lymphoma, then they may not be able to be believed. And this also fits the work of another group that published in 2011, that, came up with a diagnostic algorithm to differentiate from lymphoma from inflammation in feline small intestinal biopsy samples.

And this is the algorithm that they came up with. And this basically says the same thing that, the first study showed in that if you have, a sample, and histopathology, tells you that it is lymphoma, or if you mean the histochemistry tells you it's lymphoma, then you can believe the diagnosis and, treat accordingly. However, if, it does not give you a diagnosis of lymphoma, then, par should be performed as well to make the final differentiation between lymphoma and inflammation.

Therefore, it is, potentially, advisable to perform all three tests in a step-wise fashion before we can be certain of the diagnosis. OK, so we've talked a little bit about diagnostic techniques of feline lymphoma. And the last part of the talk now is just going to focus on staging feline lymphoma.

So staging is the process where the extent of the disease in the body is assessed. And a good staging scheme should give accurate prognostic information. There are a couple of staging schemes, used.

So the WHO has a staging scheme for, lymphoma in domestic animals. And there is also the Ann arbour scheme, which is the most widely used staging scheme for lymphoma in math. So this is the WHO staging scheme for lymphoma in domestic animals, which some of you may be aware of.

And so it starts with, stage one, where a single lymph node or lymphoid tissue in a single organ is affected, moving through, to generalised lymph node involvement, and liver and spleen involvement. So stage 3 and stage 4 are the most common presentations of canine multicentric lymphoma. And then stage 5 is manifestation in the blood and involvement of the bone marrow and other and or other non lymphoid organs.

Now, hopefully, some of you have realised that the problem in cats is that because extranodal non-lymphoid organ lymphoma is so prevalent, that that automatically puts a lot of cats with lymphoma into the stage 5 category. And that's not really very helpful if we're thinking that stage 5 animals have the worst prognosis, as, again, we know that that's not the case in cats. So the problem in cats, therefore, is that staging schemes are have not been shown to be particularly prognostic.

And this is a staging scheme that was, developed, for cats, in the 80s, which is a bit of an adaptation of the Ann arbour scheme, looking kind of whether the lymphoma is sort of in one region of the body, so above the diaphragm or if it's spread to below the diaphragm as well. But again, this has not been shown to be particularly useful in predicting outcome in feline lymphoma. Another part of staging is, given, affected animals a substage A or substage B classification, and that means essentially whether they present with clinical signs or not.

Again, in man and in dogs, if they present with substage B disease in Normally have a worse prognosis. However, the problem is, as I've already mentioned, nearly every catch of lymphoma will present with a clinical sign, and therefore, technically, they are all substage B. The only exceptions to this are probably the cats with Hodgkin's lymphoma, where the, present with, otherwise well, but just with one or two enlarged lymph nodes.

And we have seen many, many cats with, come in with significant clinical signs and quite widespread disease that still have done very, very well with treatment. So the staging, in order to predict prognosis does not seem to be particularly useful. So the question therefore is, should we stage at all?

Is there any point in staging cats or is it just a waste of money? Well, there are some arguments for staging cats, some of which are more important than others. The first argument is a little bit of an academic one, but I think it is still an important one.

If, at the moment we don't have a good staging scheme for cats with lymphoma. However, we will never generate a good staging scheme unless we have the data to do that. And therefore, the argument is that we should be staging our cats to generate that data, and therefore, hopefully enable us to make a better staging scheme in the future.

The second reason to stage cats is because it might . You might discover another problem. And this is particularly common in, our older cats who might have concurrent heart disease or chronic kidney disease.

And this might affect the treatment that you are wanting to prescribe. So, for example, an animal, with nasal lymphoma, but severe hypertrophic cardiomyopathy probably is not a patient, you are going to recommend for, radiotherapy as we need to perform multiple anaesthetics in that animal. Just a quick note about bone marrow involvement.

This usually isn't part of a, a, a staging workup in cats because actually most cats don't have bone marrow involvement. However, if you have a cat with, peripheral cytopenias, then it might be useful to perform. One instance where we definitely need to stage our patients thoroughly is with, if we are thinking about performing a local treatment for isolated disease.

So the two best examples of this would be a Hodgkin's-like lymphoma, where you have one, for example, enlarged submandibular lymph node in the patient. Or another good example would be nasal lymphoma. So for the cat with the Hodgkin's lymphoma and the one enlarged lymph node, we might be considering surgical excision of that, of that node.

For the cat with nasal lymphoma, we might be considering radiotherapy. However, we need to make sure that, the, cats do not have any. A systemic disease before we embark on the local therapy.

This is because our treatment may otherwise fail. So, a good example of this is this paper that was published this year, which showed that 30% of cats that received radiotherapy for their nasal lymphoma relapsed at an extra nasal site outside of the radiation field. So it's therefore likely that these cats had lymphoma somewhere else that was not picked up on the initial, investigation.

They, the cats have then undergone extensive radiotherapy treatment. The owners have potentially spent all of their money, for the cat to relapse somewhere else. And the, and cats that have any distant disease should probably be treated with radiotherapy, either in combination, sorry, should be treated with chemotherapy, either in combination with the radiotherapy or as a sole treatment.

So, as I have kind of touched on, looking at trying to predict the outcome in feline lymphoma, it is difficult. Staging schemes don't really seem to provide much information for the prognosis in feline lymphoma. Anatomical site and grading can provide some prognostication, so for example, the difference between high grade and low grade intestinal lymphoma.

However, we know one of the biggest prognostic factors is actually response to treatment. And several studies have shown that cats that achieve a complete response have a much more favourable outcome than cats that only have a partial response. So when we're trying to convince our owners to treat their cats with, whatever treatment you're, advising, they, unfortunately have to bite the bullet and see whether the treatment's going to be work before we can give them a better idea of prognosis.

Studies have shown that progressive weight loss and anaemia, despite treatment are poor indicators, and this is most likely because you have not got the lymphoma under control. So, in summary, feline lymphoma represents a diverse range of diseases. The diagnostic approach is determined by the anatomical site, and histology is often required to achieve a definitive diagnosis.

Useful staging schemes to give us prognostic information are lacking, however, staging is often a good idea, particularly as it can influence the type of treatment that we can, offer to our patients. Thank you very much. I'm open to any questions.

OK, thank you very much, Aaron, that was really interesting. So I will just give you guys a couple of minutes. I've got one question that's come through already, so I'll just give you guys a couple of minutes just to type in any questions in that question and answer box, and we'll get, we'll get them put to Aaron straight away.

I will just take this little opportunity just to give you the date for the Sarah Mason, webinar is on the 21st of November, and she'll be discussing feline lymphoma, and it's a case-based management and treatment. And just a bit of shameless self promotion for my own webinar on the 19th of November. I'll be discussing chemo chemotherapy safety in practise.

So. It's kind of nice that November we've managed to have quite a few, oncology, chemotherapy webinars all presented. So we've got, I've said, we've just got one, question come through, and this is from Alistair, and he's asking how common is leukaemia in lymphoma cats?

And he's asking any prognostic value, which I'm, I'm wondering whether that that means if there's a, how much of a difference in prognosis it is if it's cat is positive for leukaemia as opposed to negative. So, now, we, I, I still do see some cats with the feline leukaemia virus, and actually one of the interesting things will be how much the, sort of the anti-vaccination feeling at the moment means that FERV might become more prevalent. But I still see a few of them.

I don't know if there's been a very recent study, epidemiologically speaking, looking at the prevalence, . There was a, a, a paper is just, this is just a random ramble. Sorry.

There is a paper that's just come out from Brazil, where the incidence of leukaemia virus in their cat is still very high, so they're still seeing a lot of lymphoma. Prognostically, the cats with FERV, infection are not supposed to do as well. You, the lymphoma does tend to, responds to chemotherapy, but they quite often have a poorer prognosis either to the, the, the Development of other diseases or general immunosuppression in general.

And those are the cats that often can also go on to develop myelodysplastic diseases and that kind of thing. So, the owners have to think very hard about whether they want to, to treat, treat a cat, an FELV positive cat. On the flip side, if you have an FIV positive cat with lymphoma, their prognosis is unchanged compared to normal, so I would go ahead and treat those guys.

OK, thank you very much. So one more question coming through from Ellis, so they've got an older diabetic cat that has been reasonably well controlled and has developed a chronic diarrhoea with no weight loss. Is this potentially an elementary lymphoma?

Yeah, potentially. I mean, any, any cat with chronic intestinal signs, any old cat with chronic intestinal signs could well have a, a low grade elementary lymphoma, absolutely. And I would kind of go through the basics in terms of ruling out hyperthyroidism and doing faecal analysis and all the sort of easy things first.

But then the next step, if the owners wanted to, would be investigating, biopsying for this cat for a diagnosis. The big problem with a diabetic cat, in this situation is, . If the cat either has a low-grade lymphoma or, just inflammatory bowel disease, you're probably not gonna want to use steroids in the cat because it'll upset its diabetic control.

So that's when you're gonna maybe think about using a single agent for ampicil or something like that, to control the disease. If it is just inflammatory bowel disease, potentially the other option would be something like cyosporin, which might help to control the clinical signs, but that won't do much if it has got lymphoma. OK, thank you very much.

So that's all the questions we've had come through from, from this evening. So I'd like to take this opportunity, Aaron, just to say thank you very much for a really interesting talk this evening. And thank you to everyone who has attended tonight, and thank you for Dawn in the background at webinar vet who's doing all the technical stuff for us.

So yeah, thank you very much and I hope you all have a lovely evening. You take care.