Lymphoma
Cancer of lymphocytes (immune cells), one of the most common cancers in dogs and cats. Often responds well to chemotherapy.
Lymphoma is the most common cancer in many breeds of dogs and is also common in cats. It is a cancer of lymphocytes — white blood cells in the immune system — and can arise in lymph nodes (most common in dogs), gut (most common in cats), liver, spleen, bone marrow, or other sites.
In dogs, the most common form (multicentric lymphoma) presents as enlarged lymph nodes — often noticed under the jaw, in front of the shoulder, or behind the knee. The pet is often otherwise well at diagnosis.
In cats, gastrointestinal lymphoma is most common, presenting as chronic vomiting, diarrhoea, weight loss — clinically very similar to IBD, requiring biopsy to differentiate.
Treatment with chemotherapy is well-tolerated in pets compared with humans. Dogs commonly achieve 12–14 months of high-quality life with combination chemotherapy; small-cell lymphoma in cats can have 2–3 year median survival with chlorambucil and steroids.
Without treatment, prognosis is months. Quality of life with appropriate treatment is usually good — most pets tolerate chemotherapy with mild side effects.