Lymphoma is the most common cancer diagnosed in cats. It’s a malignancy of lymphocytes, a type of white blood cell found throughout the body, which means it can develop in nearly any organ or tissue. The gastrointestinal tract is the most frequently affected site, but lymphoma can also arise in the chest, kidneys, nasal passages, skin, and lymph nodes. Understanding the type, grade, and location of your cat’s lymphoma matters enormously because these factors shape both treatment options and expected outcomes.
How Lymphoma Develops
Lymphocytes are immune cells that normally patrol the body looking for infections and abnormal cells. In lymphoma, genetic mutations cause these cells to multiply uncontrollably. Research has identified several key mutations involved, including changes in genes that normally act as brakes on cell growth. One of these, the TP53 gene, is the same tumor-suppressing gene most commonly mutated in human cancers. When it stops working properly, damaged cells that should be destroyed instead survive and keep dividing.
In the most common subtype of feline intestinal lymphoma, about 17% of tumors carry a specific mutation that drives abnormal cell signaling. This particular mutation is also found in a similar type of intestinal lymphoma in humans, which has helped researchers understand feline lymphoma better and explore treatments that may cross over between species.
Types of Feline Lymphoma
Veterinarians classify feline lymphoma by two main criteria: where it grows and how aggressive the cells look under a microscope.
By Location
The four traditional anatomical forms are:
- Alimentary (gastrointestinal): The most common form, centered on the stomach, intestines, and sometimes the liver or surrounding lymph nodes.
- Mediastinal: Develops in the chest, typically involving the thymus or lymph nodes between the lungs. This form is strongly linked to feline leukemia virus (FeLV) infection and tends to affect younger cats.
- Multicentric: Involves multiple lymph nodes throughout the body simultaneously.
- Extranodal: Appears in organs not typically associated with the lymphatic system, such as the nasal passages, kidneys, skin, or nervous system. Nasal lymphoma is one of the more treatable extranodal forms.
By Grade
The most important distinction is between small cell (low-grade) and large cell (high-grade) lymphoma. Small cell lymphoma grows slowly and follows an indolent course, sometimes progressing over months or even years before causing obvious symptoms. Large cell lymphoma is aggressive, progressing quickly and requiring more intensive treatment. Your vet will determine the grade through tissue sampling, and this single factor often matters more than anything else in predicting how your cat will respond to treatment.
Risk Factors
Feline leukemia virus remains one of the strongest risk factors. In one study of lymphoma cases where viral status was tested, 75% were FeLV-positive. The virus showed a particularly strong connection to mediastinal lymphoma, with younger, FeLV-positive cats being the most likely to develop this chest form. Feline immunodeficiency virus (FIV) also increases lymphoma risk, though it’s associated with a different pattern: typically high-grade, B-cell tumors that appear in unusual locations like the nasal passages.
Widespread vaccination against FeLV over the past few decades has shifted the landscape of feline lymphoma. The mediastinal form that once dominated has become less common, while alimentary lymphoma in older, virus-negative cats has become the most frequently diagnosed type. Most cats diagnosed with gastrointestinal lymphoma today are middle-aged to senior and test negative for both FeLV and FIV.
Symptoms to Watch For
Because lymphoma can appear in so many locations, the symptoms vary widely depending on the form.
Gastrointestinal lymphoma, the most common type, typically causes weight loss, decreased appetite, vomiting, and diarrhea. These signs often develop gradually, especially in the small cell form, and can look identical to inflammatory bowel disease. Many owners notice their cat slowly losing weight over weeks or months before other symptoms become obvious. Weight loss before treatment begins is actually a meaningful prognostic sign: cats that have already lost significant weight before starting therapy tend to have shorter survival times.
Mediastinal lymphoma can cause difficulty breathing, open-mouth breathing, or a noticeably faster respiratory rate as fluid or tumor mass compresses the lungs. Some cats cough or lose their appetite. Nasal lymphoma often presents as chronic nasal discharge, sneezing, or noisy breathing from one nostril. Multicentric lymphoma may show up as painless swelling of lymph nodes under the jaw, in front of the shoulders, or behind the knees.
How Lymphoma Is Diagnosed
Diagnosis starts with a physical exam and often an abdominal ultrasound, which can reveal thickened intestinal walls, enlarged lymph nodes, or masses in the abdomen or chest. From there, the vet needs a tissue sample. Fine needle aspirate cytology, where a thin needle draws cells from a suspicious area, is the quickest first step. However, definitive diagnosis, especially distinguishing small cell lymphoma from inflammatory bowel disease, often requires a biopsy that provides a larger tissue sample for examination.
In more complex cases, additional tests may be needed. Molecular testing called PARR (PCR for antigen receptor rearrangement) can detect the clonal expansion of lymphocytes that signals cancer, even when standard cytology is inconclusive. Flow cytometry, bone marrow sampling, or imaging of the chest and abdomen may also be used to determine how far the disease has spread, a process called staging.
Treatment Options
Treatment depends heavily on the grade and location of the lymphoma. The approaches for small cell and large cell disease are quite different.
Small Cell (Low-Grade) Lymphoma
This slower-growing form is typically managed with oral medications that you give at home, usually a steroid combined with an oral chemotherapy drug. Many cats tolerate this protocol well, maintain a good quality of life, and can live for a year or more with treatment. Some cats respond so well that their symptoms resolve almost entirely.
Large Cell (High-Grade) Lymphoma
Aggressive lymphoma requires more intensive chemotherapy. The most common multi-drug protocols are based on CHOP, a combination that includes cyclophosphamide, vincristine, prednisolone, and doxorubicin. These are typically given as injections at the vet clinic, with visits every one to two weeks during the initial treatment phase. A full protocol may involve 11 or more treatment visits spread over several months.
Chemotherapy in cats is generally better tolerated than in humans. Most cats don’t lose their fur, and while mild nausea or a temporary dip in appetite is common, severe side effects are relatively rare. That said, cats with large cell lymphoma do tend to lose weight during the first two months of treatment, averaging about a 4% drop from their starting weight. Maintaining weight early in treatment is linked to longer survival.
Survival and Prognosis
In a large study of 110 cats treated with a multi-drug chemotherapy protocol, 60% achieved complete remission. The overall median survival was 274 days (about 9 months), with a one-year survival rate of 41% and a two-year survival rate of roughly 35%. Cats that achieved complete remission had a median disease-free period of 763 days, over two years.
Prognosis varies significantly by location. Mediastinal lymphoma had the highest one-year survival rate at nearly 67%, with a median survival of over 1,000 days in cats that responded to treatment. Alimentary lymphoma had a median survival of 486 days. Cutaneous (skin) lymphoma carried the worst prognosis, with none of the cats in that study reaching one year.
Small cell intestinal lymphoma, while not included in the same study, generally carries a more favorable outlook than these numbers suggest. Many cats with low-grade disease live one to two years or longer with oral treatment, and some live well beyond that.
For cats where chemotherapy isn’t an option due to the owner’s preference, the cat’s age, or other health problems, steroid treatment alone can provide temporary symptom relief and improve quality of life for a period of weeks to a few months, though it does not achieve the longer survival times seen with full chemotherapy protocols.
What to Expect After Diagnosis
If your cat has been diagnosed with lymphoma, the next steps typically involve staging to determine how far the disease has spread, followed by a conversation with your vet or a veterinary oncologist about which treatment approach fits your cat’s specific situation. The grade of the lymphoma, your cat’s overall health, and practical considerations like visit frequency and cost all factor into the decision.
Monitoring during treatment relies heavily on repeat imaging, bloodwork, and tracking your cat’s weight and appetite at home. Because most feline lymphomas are internal, you often can’t see or feel the tumor directly, which makes these check-ins important for gauging whether treatment is working. Cats that maintain or gain weight in the first month of chemotherapy consistently do better than those that continue losing weight, so keeping your cat eating well during treatment is one of the most meaningful things you can do at home.