Dog HealthCat HealthVeterinary Term
What Is Lymphoma?
Definition
Lymphoma is a cancer of the lymphatic system — originating in lymphocytes (a type of white blood cell) found in lymph nodes, the spleen, bone marrow, and other organs. It is one of the most common cancers in dogs and cats. While serious, lymphoma in dogs is among the most treatable cancers — many achieve remission with chemotherapy, with a median survival of 12–14 months.
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Understanding Lymphoma
Dogs most commonly develop multicentric lymphoma — simultaneous swelling of multiple lymph node groups throughout the body. The enlarged lymph nodes (under the jaw, in front of the shoulders, behind the knees, in the groin) are typically firm, painless, and can be felt by an owner. This form most commonly responds well to CHOP-based chemotherapy protocols. Other forms include gastrointestinal lymphoma, which causes vomiting, diarrhoea, and weight loss, and mediastinal lymphoma, which causes breathing difficulties.
In cats, lymphoma most commonly affects the gastrointestinal tract rather than the lymph nodes, causing chronic vomiting, weight loss, and diarrhoea in older cats. It is also the most common cancer associated with feline leukaemia virus (FeLV). Feline GI lymphoma is classified as low-grade (indolent) or high-grade (aggressive) — low-grade GI lymphoma has an excellent response to oral prednisolone and chlorambucil, with many cats achieving remission for 2+ years.
Diagnosis requires cytology (fine needle aspirate of an enlarged lymph node or mass) for an initial assessment, typically confirmed by biopsy and histopathology. Immunophenotyping (B-cell vs T-cell classification) is important because B-cell lymphoma has a significantly better prognosis than T-cell in dogs. Staging includes bloodwork, urinalysis, chest X-rays, and abdominal ultrasound to assess spread and organ involvement.
📌 Key Facts
Most common form in dogs
Multicentric (multiple lymph node groups enlarged)
Most common form in cats
Gastrointestinal (vomiting, weight loss)
Dog chemotherapy response rate
80–90% achieve remission
Low-grade cat GI lymphoma
Excellent response to oral medication — often 2+ years remission
Frequently Asked Questions about Lymphoma
I can feel swollen lumps under my dog's jaw and behind their knees — could this be lymphoma?
Simultaneous firm, painless swellings at multiple lymph node locations in a dog is a classic presentation of multicentric lymphoma. This warrants an urgent veterinary assessment — a fine needle aspirate of one of the nodes provides a rapid answer. Early diagnosis and prompt treatment improve outcomes significantly.
Is chemotherapy for dogs the same as for humans?
Many of the same drugs are used, but the protocols are designed for dogs and the dosing approach differs — veterinary oncologists generally prioritise quality of life by using doses that are effective without causing the severe side effects common in human cancer treatment. Most dogs undergoing chemotherapy maintain good quality of life and many owners report their pets seem unaware of being on treatment.
My older cat has been losing weight and vomiting for months — could this be lymphoma?
Chronic vomiting and weight loss in an older cat has several possible causes — hyperthyroidism, inflammatory bowel disease, and GI lymphoma are among the most common. These conditions can also be very difficult to distinguish without biopsy. A vet assessment with bloodwork, ultrasound, and potentially intestinal biopsy is needed to reach a diagnosis. GI lymphoma in cats, particularly low-grade, is often highly manageable.
⚠ Medical Disclaimer: This glossary entry is for educational purposes only
and does not constitute veterinary advice. Always consult a licensed veterinarian for diagnosis
and treatment of your pet's health conditions.