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May 4, 2023 — Dr. Kelly Diehl chats with Dr. Emily Rout from the Clinical Hematopathology laboratory at Colorado State University about lymphoma in dogs and cats. The pair focus on diagnosis of lymphoma as well as what the team at CSU is learning about new subtypes of this cancer in dogs. The pair also touch on other blood abnormalities that can look like lymphoma but are benign.



0:00:10.3 Kelly Diehl: Welcome to Fresh Scoop, Episode 56, Lymphoma in Dogs and Cats. I'm your host, Dr. Kelly Diehl, Morris Animal Foundation, Senior Director of Science Communication. And today, we'll be talking with Dr. Emily Rout. Dr. Rout is a clinical pathologist and research scientist in the Clinical Hematopathology Laboratory at Colorado State University. That's a mouthful. Welcome, Emily.

0:00:35.0 Emily Rout: Hi, thank you for having me.

0:00:40.1 KD: Before we get started, I always ask everyone to tell us a little bit about yourself and what led you to become a veterinarian and ultimately get your PhD and pursue a research career.

0:00:53.9 ER: Yeah, so I actually pursued research before I ever attended veterinary school. So, after college, I went and worked in a research laboratory at the National Institute of Health in Bethesda, Maryland. And I was working in a lab for three years that studied disorders of red blood cell development. So that experience got me interested in hematopathology. So, I was interested in research and interested in disorders of cells in the blood. So, I came to vet school with that interest and then continued to have that interest through vet school. And after an internship, I came back and did a residency in clinical pathology. And then, I pursued a PhD studying lymphoma and leukemia in the clinical hematopathology lab here at CSU. So, my PhD was on B-cell chronic lymphocytic leukemia. And then since then, I've continued to work in this lab. So, we provide diagnostic service to diagnose and subtype lymphoma and leukemia. And then I also perform research projects to study these different tumors.

0:02:05.7 KD: That sounds really, really fascinating. And I think a lot of us listening know something about lymphoma, but let's go back to some basics, because I get confused about this. And can you define a little bit what lymphoma is? And then, can you talk about how it is different and similar to leukemia? Because I get that question a lot from, for example, like my neighbors, or even other veterinary professionals.

0:02:36.9 ER: Yeah, sure. So just in a general sense, lymphoma is a tumor of lymphocytes. And that term lymphoma actually comprises a pretty diverse group of tumors. So, there are many different types of lymphoma, so different kinds all arising from lymphocytes. And lymphoma can arise in the lymphoid tissues, often in tissues like lymph node or spleen, but can also arise in other tissues in the body. And as far as lymphoma versus leukemia, there actually is a fair bit of overlap, but in general, the term lymphoma is often used to describe tumors where most of the disease is in the solid tissues like lymph nodes. And then, leukemia is often used to describe tumors where most of the disease is in the blood and/or bone marrow. But I think one of the reasons it's confusing is that sometimes we have overlap in the sites that are affected. So, for example, a common tumor type that we see in dogs is indolent T-zone lymphoma, and that's actually a really common tumor type to affect both lymph nodes and blood. So, we frequently refer to that disease actually as T-zone lymphoma/leukemia, since both sites are affected.

0:03:57.1 ER: And I think in people now, the distinction between leukemia and lymphoma is generally based on the degree of blood and/or bone marrow involvement. But for certain types of tumors in people such as B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma, they actually recognize that while some patients may have most of the tumor in the blood, and are called a leukemia, and some patients may have bulk of disease in the tissues and is called a lymphoma. Regardless of which term you use, those patients have the same disease, it's just different manifestations of that disease, if that helps. But I think it is sometimes confusing which term we use.

0:04:39.5 KD: Yeah, I have trouble sometimes with it and I've obviously learned about it a long time ago. And actually, the subtypes of lymphoma I think is going to be new to a lot of folks out there. And even though I know there are subtypes in dogs, we'll get to cats later, I was recently just blown away when I learned about how many subtypes of lymphoma there now are. I think I will date myself by saying many, many years ago when I first became a veterinarian, I heard of non-Hodgkin's and Hodgkin's in people, but there's lots more that many people may not be familiar with. So, I know that differentiating these subtypes is an important component of what you do in the lab there, but can you talk a little bit about how many subtypes there are out there and touch on it as far as what we know? And let's just do dogs.

0:05:47.4 ER: Yeah, so we do have a lot of different subtypes. There are many more in people than what we recognize in dogs, but we still do see a lot of different types in dogs. And I think it's important for us to try and classify them so that we can give accurate prognostic information, and that'll help guide treatment too. And the different types are classified based on a number of factors. So, one is just the anatomic location. So, what site in the body is affected? Is it lymph nodes or skin or the intestine? Another feature that is involved in classifying them is the immunophenotype, meaning whether they're B-cells or T-cells, and that reflects the different proteins that the cells express. And then also if histology is performed, meaning a biopsy of that tissue, the pathologist can provide what we call a WHO classification, which is also a classification system that's used in people. So, you may have heard of that in people as well, but it's a classification system that kind of takes into account the type of cells, the pattern that the lymphoma is forming in the tissue, the cell size and other criteria.

0:07:06.9 ER: And so those different factors can help them classify that type of lymphoma. And in dogs, most forms of lymphoma are nodal. And among those nodal lymphomas, meaning that they're in the lymph nodes, there are a lot of different kinds, and they have different prognoses. And some of these subtypes can be diagnosed by flow cytometry, so that's a test that we perform in our lab. So, for example, one of the common kinds of T-cell lymphoma that we see in dogs is a really aggressive form of T-cell lymphoma. That's a form that's often seen in Boxers, and they can have hypercalcemia. And those tumor cells have unique features that allow us to diagnose that specific subtype by flow cytometry. And then in contrast, there's a different type of T-cell lymphoma in dogs called T-zone lymphoma. Those cells are going to have different features that we can still diagnose by flow cytometry, but those cases actually have quite indolent disease. So those dogs may not even need treatment and can survive for years with that disease. So, I think it's important for us to subtype these different kinds. And we have different tools available to do that.

0:08:22.9 ER: So, we use flow cytometry, and that's nice because it's a little bit less invasive. We can do it on a sample of the node where we just poke the node with a needle and syringe to collect the cells. Histology is another tool that we can use to subtype these lymphomas. That's just a bit more invasive because we actually have to collect a bigger piece of tissue. So, we actually have to get a biopsy to do that. But that's kind of an overview of how we subtype them and the different tools we have available.

0:09:00.1 KD: Well, that's really helpful, Emily. I think the science here is really expanding. And if there are folks listening who may be like, "Geez, I don't know if I know very much about T-zone," I'm with you. It seems like they're changing all the time. Before we get back to dogs, let's take a quick dive into a cul-de-sac about subtypes in cats, because we know cats get lymphoma. But why have cats... I mean, are they hard to subtype? We don't have the tools? Or why do we seem to not do as much in cats, or know as much in cats?

0:09:40.5 ER: Yeah, unfortunately, we do have fewer studies characterizing lymphoma in cats. So, I think one reason may be that cats often develop lymphoma in areas that are harder to sample. So, sites, for instance, that are within the abdominal cavity, so it's just a lot harder to reach those sites. Whereas, as I mentioned, in dogs, lymphoma often presents in those peripheral lymph nodes, so lymph nodes on the outside of the body. So, it's just a lot easier to sample those sites in dogs. So, I think that might be part of why we have more studies in dogs with well-characterized lymphomas and outcome information. But like you mentioned, I also think that we have fewer tools available. So, by flow cytometry, we rely on having antibodies that work in that species to help us characterize the different types of lymphocytes in that sample. And unfortunately, in cats, we have far fewer antibodies available to characterize the lymphocytes. And so, that makes it a lot harder for us, in cats, to subtype lymphoma and leukemia. And so, I think we aren't able to recognize as many subtypes and we don't know as much about them. And then I also think that there's been less work in cats to try and describe things like the gene expression profile and mutations in feline lymphoma.

0:11:10.0 ER: In the dog, our group and others have been sequencing these canine tumors to try and better characterize them genetically and compare them to human tumors. So, I think we're just a little bit further behind in doing this with cat tumors, but certainly that's something that we're working on now, and so are other groups too.

0:11:31.7 KD: Okay. Emily, you did a great thing for me in that you gave me a terrific lead into a question I wanted to ask, which is, I know it's a broad topic, but can you tell us some of the important differences between lymphoma in cats and lymphoma as we see it most commonly in dogs?

0:11:51.3 ER: Yeah, a major difference is the sites that are affected by lymphoma between the two species. So, in dogs, the most common form of lymphoma that we see is in the lymph nodes. So, dogs that have lymphoma frequently present with enlarged peripheral lymph nodes, but in contrast in cats, it's really unusual for us to see lymphoma present in peripheral nodes. So, that's a big difference. Instead, the most common form of lymphoma that we see in cats is actually in the gastrointestinal tract. So, there are a few types of GI lymphoma that we see in cats, but a low-grade, small cell T-cell intestinal lymphoma is the most common form, but that's a form that is much less commonly seen in dogs. So that's a big difference. And then another difference too, this is a little bit more historic, but in cats, we also used to see lymphoma that was frequently associated with FeLV infection, which isn't something that we'd see in dogs. But that's actually not a major cause of lymphoma anymore in cats as we work to eliminate and vaccinate against that disease.

0:13:03.9 KD: Right, and as an older practitioner and a person who had cats for a long time, I can remember pre... When feline leukemia virus was more prevalent and vaccines were just coming out, and we lost a young cat, my parents did, with lymphoma that was mediastinal. So, a big lymph node in the chest, for those of you guys who don't know it. And then I have lost a cat since then, many years later from the intestinal form that you're talking about. You talked about the World Health Organization, WHO, and how they classify tumors. And there are probably folks out there who've either had a pet with cancer or have had cancer themselves, and they often talk about staging. We don't really do that, or I never did it in cats. But can you talk a little bit about how lymphoma is staged in dogs? because it's super important in prognosis and treatment.

0:14:06.9 ER: Yeah, so the staging system takes into account which anatomic sites in the body are involved and affected by the tumor. And then, it's also taking into account whether the patient has clinical signs or not. So, a lower stage, so stage one means that the tumor is limited to just a single lymph node. And then as you progress to higher stages, it means that more sites in the body are affected by that tumor. So, stage two means that there's actual multiple nodes affected, but just in a regional area. And then as you get higher, so for example, stage four means that liver, spleen are involved, and stage five means that bone marrow or other organ systems are involved. So, it gives you a sense of how widespread the disease is. And for certain types of lymphoma, a more advanced stage is associated with a worse prognosis. So, that's important information to have as far as what prognosis to expect and may change the treatment plan as well. And then the sub-stage refers to whether or not the patient feels well or not, so whether they have clinical signs. And those patients that present feeling sick are associated with having a worse prognosis.

0:15:34.9 KD: And that's really helpful. And correct me if I'm wrong, but here's where I think it's really hard to explain to people. Stage five lymphoma, as you've mentioned, means the bone marrow is affected. And then we can see weird lymphocytes in the blood. And this is where that whole leukemia, lymphoma thing sometimes gets confusing for people, I think. Is that correct or am I oversimplifying that?

0:16:00.3 ER: No, I think that that is really hard, because for a disease like T-zone, even though that's a pretty indolent disease, they frequently have those neoplastic lymphocytes in the blood. So, by some staging systems, because the blood is involved, they would consider that stage five, which is implying a higher stage and more aggressive disease. But we actually don't think that T-zone cases that have T-zone cells in the blood do have a worse prognosis. So, I think that's why for certain tumor types, the stage may be more useful than others. But you're right that for some diseases, having the presence of the tumor cells in the blood may not affect the prognosis.

0:16:48.2 KD: That's a really good point. I never thought about that with T-zone because that does kind of turn that staging or what we typically tell people, which is, if they're... For picking up abnormal cells in the bloodstream, that can be a big problem. And that... Oh, I just gave myself the best segue ever [chuckle] into a question I was going to ask. And this is actually something that we at the Foundation were involved with and a project you guys did. So, we're talking about lymphocytes, which are white blood cells, they're in the bloodstream, they're normal. But sometimes, they get wonky. And you guys found something in English bulldogs with wonky lymphocytes. Can you talk about that research and what you found and why it's important?

0:17:39.0 ER: Yeah, I think this is a really interesting syndrome that we discovered in English bulldogs where they have an expansion of non-neoplastic B-cells in the blood. So, they'll have increased numbers of B-cells there, but they actually don't have cancer. So normally, when we see expanded B-cells in the blood, it's consistent with a form of cancer called B-cell chronic lymphocytic leukemia. But we found that in these bulldogs, the expanded B-cells in the blood actually aren't clonal, they're actually reactive or non-neoplastic. So, this was really important for us to discover, because historically we would have thought that these bulldogs had cancer when in fact they have a non-neoplastic disease. And we looked at this syndrome and worked to describe the clinical presentation of this disease. And we found that these dogs are often young. So sometimes, these bulldogs are as young as two years old when they're diagnosed. And they will frequently have other clinical signs in addition to just having increased B-cells in the blood. So, they often have big spleens, and then they can also have increased immunoglobulin protein in the serum, so antibodies that could be increased in the serum.

0:18:57.0 ER: And then it does seem to be an indolent disease, so these dogs can live for years without progression, and we've now followed some of these dogs for a few years. But sometimes, they do still need treatment, especially if they have really big spleens that are causing discomfort or if they're having clinical signs, which we can see associated with hyperglobulinemia. Sometimes, even though they don't have cancer, they may still need some kind of treatment to control this disease that they have.

0:19:30.0 KD: Okay, so the big... For people who are listening, if you happen to have an English bulldog, the big concern would be that these guys could be inaccurately diagnosed as lymphoma, correct, Emily?

0:19:44.5 ER: Yeah, yeah. So, we could see increased lymphocytes on their blood work and be worried that they have cancer, when in fact they don't have cancer, they have this other syndrome where they have increased non-neoplastic B-cells.

0:20:00.4 KD: Okay. And actually, I misspoke there. So, either stage five lymphoma or leukemia. So, I think you just gave a good reason why your lab, it's important for everyone who's listening and has a dog that may be diagnosed with lymphoma or leukemia to really sort that out a bit more using some of the tests that you guys run there at CSU.

0:20:23.3 ER: Yeah. And actually, there's another... This is actually a tumor that we described in young English bulldogs, that's a tumor of T-cells rather than B-cells. And that tumor, unfortunately, is really aggressive even despite chemotherapy. And it also affects young bulldogs, so they're often only two or three years of age as well. And so those can actually present similarly, where you're going to see increased lymphocytes on blood work, but it would be really important to do additional testing like flow cytometry to determine whether this young bulldog has this aggressive T-cell tumor versus this B-cell syndrome that isn't even cancer. So, you may see that abnormality on blood work, but it would be really important to do additional testing to figure out the cause.

0:21:16.2 KD: Right. And maybe you can't answer this, Emily, but is this something new? Do you have any historic perspective from the lab there about bulldogs in the past? Is this something creeping into the breed or something we're just recognizing?

0:21:35.9 ER: I imagine that bulldogs were getting this disease historically, and we didn't realize it. I do think we might be seeing it now more because these dogs are just perhaps getting blood work more often, and then if there's a minor abnormality such as a minor increase in lymphocytes on blood work, people are pursuing additional testing more than perhaps they were in the past. So, I do think we may be seeing an increased number through our lab, but I think that may also be just a reflection of people being a bit more proactive and trying to investigate these changes on blood work, perhaps more than we used to.

0:22:23.9 KD: Right. And dovetailing off of that very, very briefly, Emily, I think we could put in another commercial for cats here. [laughter]

0:22:33.9 ER: Sure.

0:22:35.0 KD: Cats also do some weird... They can get high lymphocyte counts too that are not necessarily cancerous. And I know this may have preceded your time at the lab, but your lab put something out, I think several years ago, and it was another Foundation-funded project where you guys looked at lymphocyte count in cats that you guys looked at. They can have pretty big counts, right? And not have cancer.

0:23:01.7 ER: Yeah, yeah. So, we see what we would call a reactive lymphocytosis, meaning an expansion of lymphocytes that's due to a reactive or inflammatory process rather than cancer. We see that happen more often in cats than we do in dogs. So, we did do a study where we looked at a large number of cats that had increased lymphocytes in the blood, and we found that a lot of them didn't have cancer, but their lymphocyte count could still get pretty high. So that was a really useful study because we now recognize that cats will develop this reactive lymphocytosis far more than I think we realized, or we see in dogs.

0:23:41.0 KD: Right. So, cat parents out there, if you ever get told you have a high lymphocyte count, it's worth pursuing but it's not necessarily something bad. Who would have ever thought English Bulldogs and cats would... [chuckle] Common ancestor? I don't know. And no one who's listening go out and say, "Kelly Diehl says bulldogs and cats are somehow related, but [chuckle] in some weird way." But tell us what you're working on right now, Emily, there in the lab? What are some of your research projects focused on?

0:24:17.3 ER: Two current products we have that I'm excited about are small cell B-cell lymphoma project in dogs, and then also an intestinal lymphoma project in cats. So, for the dog project, we're trying to learn more about these small cell B-cell lymphomas that affect the lymph nodes of dogs. So historically, we thought that small cell lymphomas were more indolent. But recently, we've discovered that a lot of these small B-cell lymphoma tumors are actually more aggressive than large B-cell lymphoma. So, these tumors can have shorter survival, and they can also be frustrating to treat because some have poor responses to chemo. So, we'd really like to learn more about these tumors. We don't really know as much about small cell B-cell lymphomas. So, we're sequencing dogs that have small cell B-cell lymphoma in the lymph nodes, and we're going to do gene expression profiling and look for mutations. And then we'll correlate that with the outcome of these patients. And we're hoping that we might find mutations that are prognostic, so that we can refine the prognostic information we give in these cases. And then also hoping that we'll find pathways that could be targeted for treatment to try and improve outcomes in these dogs with these aggressive tumors. And then we are...

0:25:40.8 KD: Oh, can I ask you something real fast, Emily?

0:25:44.4 ER: Yeah.

0:25:45.1 KD: What are you seeing? Are there breed predisposition, sex, age for those aggressive small cell B-cell lymphomas?

0:25:53.6 ER: We actually... For these nodal, small cell B-cell lymphomas, we haven't seen particular breeds affected. It's been a mixture of males and females, and they're often in middle-aged to older, so kind of similar to what we see in our large B-cell lymphoma. So, we haven't had a breed stick out in particular for these.

0:26:16.8 KD: Okay, thanks. Sorry to interrupt you. [chuckle]

0:26:19.4 ER: No, that's okay. And I think part of the study is that we are seeking... This is a prospective study where we're enrolling these cases as we see them, so we are going to enroll a large number of cases, and hopefully, those are the types of questions that we can investigate. But so far, I haven't noticed any striking breed differences. And then for the cat project, we're really interested in studying intestinal lymphoma in cats in our lab to try and improve our diagnosis of this disease and also better understand what causes the development of intestinal lymphoma. So, it's fairly common for cats to develop chronic GI signs, so things like vomiting, diarrhea and weight loss. And two differentials for that are inflammatory bowel disease and intestinal lymphoma. And those diagnoses can actually be really challenging for us to differentiate, and sometimes, it's a frustrating diagnosis to try and make. So, we're looking at the correlation of different diagnostic tests to see if we can improve our ability to distinguish IBD from intestinal lymphoma. So, for this project, one of the internal medicine doctors here at CSU, Dr. Craig Webb, has been collecting intestinal biopsies from cats with chronic GI signs. I think we have about 160 cats now.

0:27:45.3 ER: And these cats represent a spectrum of patients, so some have IBD and some have definitive lymphoma, and then there's a bunch in between that have suspicion of lymphoma. And we're doing histology on these. We also do a test called PARR that assesses whether the lymphocytes in the sample are clonal and thus neoplastic. And then we're also looking for specific mutation that's been described in feline intestinal lymphoma called STAT5B mutation. And through these different diagnostics, we're hoping that we can refine how we diagnose IBD and lymphoma. And then we're also going to sequence the intestinal biopsies of these cats to see what changes we see in gene expression and mutations between the cats with IBD and the cats with lymphoma, and hopefully, this will help us to better understand what drives development and progression of lymphoma in these cats.

0:28:44.5 KD: That sounds really cool. As a gastroenterologist, that was... When I was in practice, I saw a lot, a lot, a lot of those cases where we weren't sure. The good news is, as you know, sometimes cats with small cell lymphoma do okay in their intestine. And if they have large cell, it's a whole different ball of wax. But it's... Yeah, it's been... That's like a holy grail, isn't it? [chuckle] In veterinary medicine. We have been trying so long to figure it out, so I hope maybe you guys figure out. Which brings me to another question, which is, what are some of those big questions? We talked about obviously small cell lymphoma in cats versus IBD, but what are some of those other ones that you'd like to tackle in the future?

0:29:37.5 ER: I think a big goal for us is to try and better characterize these lymphomas genetically. So, many of the subtypes of lymphoma and leukemia in people are classified based on the mutations that they carry, or the pathways that are dysregulated. And by identifying those abnormalities that are driving those tumors in people, they can target them with inhibitor therapies, so very targeted specific therapy and improve outcomes. And that's something that I think we'd really like to be able to do in our veterinary patients. So, for example, in people with CLL, the CLL tumor cells are reliant on B-cell receptor signaling, and they have different inhibitor drugs that can block that signaling, which has really revolutionized the therapy for B-cell tumors in people. And if we could identify pathways like that that are crucial for tumor survival in our veterinary patients, I'm hoping that eventually, we could move beyond chemotherapy to more targeted therapies and hopefully improve outcomes for a lot of these different types of lymphoma and leukemia that we're seeing.

0:30:52.5 KD: That would be really amazing because having had... You can't have pets and not have had pets suffer from lymphoma. And I've had a cat with cutaneous lymphoma, which is an absolute nightmare. I mean, she died within four weeks of diagnosis, and I was a veterinarian. It's terrible. I have had a cat... My parents had the cat I mentioned with lymphoma that was probably... It was a FeLV positive cat, 1986, mediastinal, also pretty horrifying. I had a dog with GI lymphoma. So, you guys who are listening heard Emily and I speak about it in cats. Well, in dogs, it's lousy. It's a terrible, terrible form of lymphoma, hard to treat, not so easy to diagnose, so we got lucky. And so, I think any of us have had to deal with this in our pets. It can be really heartbreaking. It can be financially tough for folks to treat. I get it. With my dog, if I hadn't been a veterinarian, it would've certainly put an even bigger strain on our finances. So, I think, Emily, what you're talking about sounds so exciting, and I'm hoping it leads to some differences in how we can care for our pets. And so, what's your take-home message? You've been studying this disease for a long time, what would you tell people who are listening?

0:32:25.2 ER: I think a major take-home is that there are lots of different kinds of lymphoma and leukemia out there. So, if you have a pet that's diagnosed with lymphoma, know that there are additional tests we can do to try and determine what kind, which may help to give more accurate prognostic information and may help guide treatment plans. In some cases, lymphoma can be really challenging to diagnose. So, in those tough cases, sometimes we need multiple tests to achieve a diagnosis, which I know can be really frustrating. But sometimes, these are really challenging tumors, I think. And then I guess like we talked about, I'm just really excited about all the research that we're doing on lymphoma, and other groups as well, to try and improve the way that we diagnose these tumors and understand the mechanisms driving them. And hopefully, that'll ultimately allow us to improve treatments for lymphoma and leukemia in dogs and cats.

0:33:30.0 KD: Well, that's awesome. Emily, before we wrap up, I wanted to ask you, you mentioned your prospective studies that are going on in the lab. If people are listening, is there information they can get? Or are you full? Or, if they're interested... Or where could they learn more?

0:33:48.9 ER: Yeah, they could always contact us at the Colorado State University Clinical Hematopathology Lab. We have a website that you could go to learn more about our lab and some of the studies and papers that we published. And then we also have contact information on there, and people are always welcome to contact us to learn more about our current studies and, I guess, eligibility criteria for those.

0:34:19.5 KD: That's awesome. Well, thanks so much. Well, and everyone, that does it for this episode of Fresh Scoop. And once again, a big thanks to Dr. Emily Rout for joining us. And of course, we'll be back with another episode next month that we hope you'll find just as informative, because we know the science of animal health is ever-changing and we need cutting-edge research information, whether we're treating patients or we're veterinary caregivers, or as pet parents. And that's, of course, why we're here. You can find us on iTunes, Spotify, Google Podcasts and Stitcher. And if you like today's episode, please take a moment to rate us because that really helps other folks find our podcast. And as always, if you want to learn more about Morris Animal Foundation's work, go to There, you'll see just how we bridge science and resources to advance the health of animals. You can also follow us on Facebook, Twitter, yes, we're still on Twitter, and Instagram. And I'm Dr. Kelly Diehl. We'll talk soon.