May 3, 2022 — Feline lymphoma is one of the most common and deadly cancers of cats. Yet it still remains difficult to diagnose and treat. Understanding what lymphoma is and isn’t in cats 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.
What’s the incidence of lymphoma in cats?
There aren’t many published statistics on how many cats are diagnosed with lymphoma each year. Many cats get sick but never receive a definitive diagnosis of lymphoma. Because some diagnostic tests are expensive, a family veterinarian may give a presumptive diagnosis based on clinical exam findings without performing further tests.
What are the most common forms of lymphoma seen in cats?
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 feline leukemia vaccination effected feline lymphoma demographics and cancer type?
The effectiveness of the feline leukemia vaccine in the reduction of this disease 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 virus, the age of cats diagnosed with lymphoma averaged 3 to 5 years. Now, in the post-feline leukemia virus 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.
How is lymphoma diagnosed?
There are a few different types of diagnostic tests to diagnose lymphoma. Some 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 all intestinal biopsies are reviewed by an experienced pathologist.
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 most 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.
What about treatment?
Even though lymphoma is a very common cancer in both cats and dogs, the course of disease, type seen and treatments used can be very 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 or not 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 also is the primary treatment for cats with Hodgkin's-like lymphoma since the cancer typically affects a single lymph node.
Lymphoma treatment and diagnosis have come a long way, but large knowledge gaps remain that 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.
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