Lymphoma (cancer that originates in the lymphocytes, a type of white blood cell) is one of the more common cancers in cats. Male cats, and cats in the Northeast in general, have an increased risk-probably related to an increased risk of feline leukemia virus. Cats who test positive for FeLV have a 60-fold increased risk of developing lymphoma, while cats who are positive for feline immunodeficiency virus (FIV) have a 5-fold increased risk for developing this type of cancer. Cats who are positive for both viruses have an 80-fold increase in their risk of developing lymphoma. Whether these viruses have a direct effect in causing the cancer or act primarily by interfering with the cat’s normal immunity is not known for certain.
The most common lymphoma sites in cats are the gastrointestinal system, the spine, and the chest cavity. The gastrointestinal type is the most common of the three forms of lymphoma and is not as closely associated with FeLV as are the other two. This type appears in older cats as weight loss and a drop in appetite. Some cats will vomit and/or have diarrhea, depending on the exact location of the cancer. Stomach cancers tend to cause vomiting and intestinal cancers are more likely to cause diarrhea. Siamese and domestic shorthairs seem to have an increased risk of developing this type of lymphoma.
The following information isn’t intended to replace regular visits to your veterinarian. If you think your cat may have feline infectious peritonitis, please see your veterinarian immediately. And remember, please do not give any medication to your pet without talking to your veterinarian first.
Mediastinal lymphoma occurs in the lymph nodes inside the chest cavity. Cats under 5 years of age who are FeLV positive are at risk for developing this type of cancer, especially if they are Siamese or one of the Oriental breeds. Fluid will build up and leads to difficulty breathing, along with regurgitation and loss of appetite.
Spinal lymphoma tends to show up in 3- to 4-year-old male cats, especially if they are FeLV positive. The first signs may be problems with their hind legs.
Diagnosing lymphoma usually requires blood tests, including tests for FeLV and FIV. Chest X-rays help with mediastinal masses and ultrasound can be helpful for abdominal growths. Spinal growths may require special dye studies, combined with X-rays or a spinal tap (removing spinal fluid for analysis).
Treatment: Surgery, radiation, and chemotherapy have all been used to treat lymphomas, depending on the exact location and whether the cancer has spread. The prognosis is best for a cat with a single intestinal nodule and worst for a cat with a spinal growth.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"