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Updated June 8, 2023 — Feline lymphoma is one of the most common and deadly cancers of cats. Yet it remains difficult to diagnose and treat. A better understanding of the disease is important if your cat is diagnosed with this type of cancer.

What is Lymphoma?
Lymphoma is a cancer that occurs when one lymphocyte (a type of white blood cell) goes rogue and acquires mutations that allow it to escape normal growth restrictions, permitting unrestricted cell division.

Incidence in Cats
There aren’t many published statistics on how many cats are diagnosed with lymphoma each year because many cats get sick but never receive a definitive diagnosis of lymphoma. And, because some diagnostics are expensive, a family veterinarian may give a presumptive diagnosis based on clinical exam findings without performing further tests.

Lymphoma Has Many Forms
Lymphoma of the gastrointestinal (GI) tract is the most common form reported by veterinarians. However, in the last two decades, veterinary oncologists and researchers have noted there are two main types of GI lymphoma, each with a different prognosis and treatment: small-cell lymphoma and large-cell lymphoma.

Less common forms of lymphoma include mediastinal (enlarged lymph nodes in the chest cavity), multi-centric nodal forms (involving multiple lymph nodes), and miscellaneous forms such as nasal, kidney and central nervous system (CNS). Extra nodal forms are much less common than GI forms.

How Has the Feline Leukemia Vaccine Helped?
Infection with the retrovirus called feline leukemia virus was at one time a major driver of the development of lymphoma in cats. However, the effectiveness of the feline leukemia vaccine in the reduction of this cancer has been astounding. Before widespread vaccination (what some veterinary oncologists call the feline leukemia era), the types of lymphoma seen in feline patients predominantly involved the lymph nodes, especially in the chest.

Before vaccination against feline leukemia, the age of cats diagnosed with lymphoma averaged 3 to 5 years. Now, in the post-feline leukemia vaccine era, cats still are tested for retroviruses, but it's uncommon to find them. The type of cancer also has trended toward GI lymphoma, and the age at diagnosis is much older, often 10 to 12 years of age.

Lymphoma Diagnosis
There are a few different types of tests to diagnose lymphoma. Certain tests are preferred if a particular type of lymphoma is suspected. It can be difficult to differentiate small-cell lymphoma from inflammatory bowel disease, so it’s important to make sure an experienced pathologist reviews all intestinal biopsies.

As a general overview, there are four main tests used for diagnosis.

  • One is cytology, where cells are collected via aspirate or biopsy and placed on a slide. This test works well for large-cell lymphoma forms.
  • Histology, which consists of examining stained sections of tissue using a microscope, is the most common way many cancers are diagnosed in both people and pets.
  • A third test is flow cytometry. This test uses a special stain to determine if cancerous lymphocytes are B cells or T cells. Learning which subtype of lymphocyte is present can influence prognosis.
  • Lastly, there is a clonality assay, which helps to determine if a pool of lymphocytes is clonal, meaning that they are neoplastic (cancerous), or if they're not clonal, indicating an inflammatory condition.

Lymphoma Treatment
Even though lymphoma is common in both cats and dogs, the course of disease, cancer type and treatments used can be quite different in cats. A general rule is that for most forms of lymphoma, chemotherapy is the treatment of choice.

In cats diagnosed with small-cell lymphoma of the intestinal tract, oral chlorambucil and an oral steroid such as prednisone are effective treatments. A few retrospective studies report excellent response rates, with many cats living several years after diagnosis.

Those reports are in stark contrast to the prognosis for the high-grade form of GI lymphoma (often referred to as large-cell lymphoma), which is treated with a multiple-drug protocol but has a poor prognosis, with most cats only living a few months even with treatment.

A few types of lymphoma aren’t treated with chemotherapy. A common example is nasal lymphoma in cats which is treated with radiation therapy. However, there remains debate among veterinary oncologists whether adjunct chemotherapy is beneficial for this type of cancer.

Cats can develop subcutaneous lymphomas, often on their distal limbs. In those cases, surgical removal with follow-up radiation therapy is used. Surgery is also the primary treatment for cats with Hodgkin's-like lymphoma since the cancer typically affects a single lymph node.

New Research Tackles Lymphoma in a New Way
As mentioned earlier, the intestinal tract is the most common lymphoma location in cats, but we still don't know a lot about how this cancer starts and why so many cats get this type of lymphoma. A research team at Colorado State University is trying to answer this question first by studying disease progression from inflammation to cancer. In the second arm of the study, the team will compare feline and human intestinal lymphoma to see if there are lessons to be learned from the way human patients are treated that could help cats too. The study is just getting started and we can't wait to see what they find!

Lymphoma treatment and diagnosis in cats has come a long way, but still lags behind what we know about the disease in dogs. These large knowledge gaps that remain affect your veterinarian’s ability to diagnose and treat the disease effectively. More research is needed to make a difference in the lives of thousands of cats diagnosed with lymphoma each year.

How You Can Help
Of course, studies like these take vision as well as financial investment. And that’s why Morris Animal Foundation, with the generous support of our donors, continues to fund this important work to change the odds for cats suffering from lymphoma. 

Follow us to learn more about how our funded animal health research is helping cats live longer, healthier lives.

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