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Lymphoma and Pets
Malignant Lymphoma in Cats
Lymphoma is the most diagnosed feline cancer. It occurs most frequently in cats already infected with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV). Cats with FeLV are 62 times as likely to develop malignant lymphoma as those without the virus, and cats with both FeLV and FIV are 77 times more likely to develop it.
Malignant lymphoma in cats tends to affect the T-lymphocytes in younger cats and the B-lymphocytes in older ones, though cats of any age can get either variant of the disease. Cats, like dogs, can develop mediastinal, multicentric, gastrointestinal and extranodal growths, but in cats, gastrointestinal growths are most likely.
Gastrointestinal lymphoma such as that experienced in cats can be classified as low or high grade. Low grade lymphomas include lymphocytic and small cell lymphoma, while high grade variants are lymphoblastic, immunoblastic, and large cell lymphoma. Low grade only occurs in the small intestine, while high grade commonly affects the stomach.
Signs and Symptoms
Malignant lymphoma in cats is likely to produce visibly severe symptoms (Compare this to dogs, which may only show enlargement of the lymph nodes). The location of symptoms will often indicate the areas of cancerous involvement, with the following types determining the most common signs:
- Gastrointestinal - Weight loss, roughened coat, and loss of appetite
- Mediastinal - Respiratory distress caused by a buildup of fluid within the thoracic cavity
- Renal/Kidneys - Enlargement of kidneys on both sides, eventually leading to renal failure
- Ocular - Anterior uveitis (inflammation of the interior of the eye) and, eventually, blindness
In addition to these symptoms, cats with FeLV will also often present with anemia-related paleness of the mucus membranes. It is important to test for FeLV and FIV in cats suspected of having lymphoma, and to biopsy the bowels to eliminate inflammatory bowel disease as a cause of symptoms.
Treatment and Prognosis
The standard treatment for feline lymphoma is chemotherapy, though gastrointestinal lymphoma can sometimes be successfully treated with prednisolone and high dose pulse chlorambucil. White blood cell counts must be measured carefully and treatment discontinued if the immune system is too severely depressed.
About 75 percent of cats experience remission of the cancer as a result of chemotherapy, although, like dogs, this is almost invariably followed by a relapse of the disease, after which further remission is unlikely. Untreated, the lymphoma can cause death within four to six weeks, and the average survival after beginning treatment is six months. In about a third of cases, the cat may survive over two years, and a very small percentage of cats are completely cured.
Cats experience fewer side effects from chemotherapy than both dogs and humans, with only five percent showing severe reactions. Cats will not typically lose their fur, though they might lose whiskers. Vomiting, lowered white blood cell count, loss of appetite and fatigue are the most common side effects, but these are typically easy to resolve, leading to an improved quality of life during treatment.