Lymphoma in Cats: The Most Common Feline Cancer and Treatment Options
Lymphoma is the most frequently diagnosed cancer in cats, accounting for roughly 30 per cent of all feline tumours. It arises from lymphocytes, a type of white blood cell integral to the immune system, and can affect virtually any organ in the body. While a diagnosis of lymphoma understandably feels devastating, understanding the condition — its forms, its behaviour, and the options available — gives you the clearest possible foundation for making decisions alongside your vet.
Why Cats Develop Lymphoma
The exact cause of feline lymphoma is rarely singular. Infection with feline leukaemia virus (FeLV) was historically the dominant risk factor, and cats testing positive for FeLV remain at significantly higher risk. However, with widespread vaccination, FeLV-associated lymphoma has become less prevalent, and today most cases occur in FeLV-negative cats.
Feline immunodeficiency virus (FIV) also elevates risk, as does prolonged exposure to environmental tobacco smoke. Research published in the American Journal of Epidemiology found that cats living in smoking households had roughly twice the risk of developing lymphoma compared to those in smoke-free homes, with risk increasing further with the number of smokers and years of exposure.
The Different Forms and Where They Appear
Lymphoma in cats is not a single disease but a spectrum, and the site of origin has considerable bearing on prognosis and treatment response.
Gastrointestinal lymphoma
The gastrointestinal tract is the most common site in adult cats, particularly in older individuals over ten years of age. GI lymphoma is further divided into low-grade (small cell) and high-grade (large cell) forms. Low-grade GI lymphoma tends to behave indolently, often mimicking inflammatory bowel disease, and carries a relatively favourable prognosis. High-grade disease progresses rapidly and is considerably more difficult to manage.
Mediastinal lymphoma
This form develops in the chest cavity and is more common in younger cats, often those with FeLV infection. Affected cats typically present with breathing difficulties and exercise intolerance caused by a mass compressing the lungs.
Renal lymphoma
The kidneys are another common site, frequently presenting as bilateral enlargement. This form has a higher rate of spread to the central nervous system, which influences both treatment planning and outcomes.
Multicentric and other forms
Lymphoma can also arise in the nasal passages, skin, spinal cord, and multiple lymph nodes simultaneously. Each location brings its own clinical picture and considerations.
Recognising the Signs
Because lymphoma can affect so many different organs, the clinical signs vary considerably. That said, common presentations include:
- Unexplained weight loss, often dramatic and progressive
- Reduced appetite or complete loss of interest in food
- Vomiting and diarrhoea, particularly with GI involvement
- Increased thirst and urination with renal lymphoma
- Laboured or open-mouth breathing with mediastinal disease
- Visible lumps along the jawline or neck in multicentric forms
- Lethargy and general withdrawal from normal activity
Many of these signs are non-specific and shared with other conditions, which is why a thorough diagnostic workup is essential before any treatment decisions are made.
Diagnosis: What to Expect
Your vet will typically begin with blood tests, urinalysis, and imaging — either radiographs or ultrasound. Ultrasound is particularly useful for evaluating the intestinal wall thickness, lymph node size, and organ architecture. Definitive diagnosis requires either fine needle aspiration cytology or a tissue biopsy for histopathology. In many cases of GI lymphoma, endoscopic biopsies offer a less invasive route to obtaining diagnostic tissue.
Distinguishing low-grade GI lymphoma from inflammatory bowel disease can be genuinely challenging, and some cats undergo treatment for one condition before a clearer picture emerges. Immunohistochemistry and PARR (PCR for antigen receptor rearrangement) testing may be used to clarify ambiguous cases.
Treatment Options
Low-grade gastrointestinal lymphoma
The standard protocol for small cell GI lymphoma involves a combination of chlorambucil, an oral chemotherapy agent, and prednisolone, a corticosteroid. This combination is administered at home, making it considerably less stressful for cats than hospital-based protocols. Response rates are high — studies report remission in 60 to 70 per cent of cats — and median survival times frequently exceed two years. Some cats live considerably longer with good quality of life throughout.
High-grade lymphoma
High-grade disease requires more aggressive multi-agent chemotherapy protocols, typically CHOP-based regimens adapted for cats. These protocols involve cyclophosphamide, doxorubicin, vincristine, and prednisolone administered in cycles at a veterinary oncology centre. Complete remission is achievable in around 50 to 70 per cent of cats initially, but median survival times are shorter, commonly in the range of six to nine months. A subset of cats achieve durable remissions beyond this.
Radiotherapy
For localised forms, particularly nasal lymphoma, radiotherapy can be highly effective. Cats with nasal lymphoma treated with radiation often achieve excellent local control and survival times exceeding one to two years are reported.
Supportive care
Regardless of the primary treatment approach, nutritional support, antiemetics, appetite stimulants, and fluid therapy all play important roles in maintaining quality of life. Cats undergoing chemotherapy generally tolerate treatment far better than people do — severe side effects are less common, and the goal remains keeping your cat comfortable and engaged with daily life.
Monitoring and Long-Term Management
Cats in remission require regular rechecks, typically every one to three months depending on the protocol. Bloodwork monitoring is important, particularly for cats on chlorambucil, which can occasionally cause bone marrow suppression. Ultrasound rechecks help assess response and detect early relapse.
Open communication with your veterinary oncologist is essential. Treatment plans are not static — they adapt based on how your cat is responding, any side effects encountered, and your own capacity and circumstances as an owner. The aim is always to balance longevity with quality of life, and an oncologist experienced in feline lymphoma will help you navigate those decisions with clarity and honesty.