Cat Could Still Have Cancer, Despite Tests

CatChannel veterinary expert Arnold Plotnick, DVM, shares his thoughts on what causes a cat's dramatic weight loss and illness.

Q: My oldest cat is wasting away. I have had him checked for cancer and thyroid but he has neither. He is, however, losing all of his muscle tissue and has gone from 14 to about 5 pounds since February.

Vets say that without extensive tests they don’t know what to do. I cannot afford more bills; I owe over a thousand dollars now. I give him a vitamin and a steroid and he eats well but continues to lose weight.

This seems similar to consumption. Does any type of consumption affect cats?

A: I cannot imagine a cat going from 14 down to 5 pounds. That is a massive amount of weight loss. In my experience, this type of weight loss is usually caused by cancer. You said you had your cat checked for cancer, but you didn’t say exactly how this was done. Blood work and X-rays, while important tests, do not always reveal cancer.

A common cause of weight loss in cats is gastrointestinal lymphoma. This cancer usually involves the small intestine. The stomach and colon are less likely to be affected. The average age of cats with GI lymphoma is 9 to 13 years old. The most common clinical signs of GI lymphoma are decreased appetite and weight loss. Vomiting occurs in about 50% of cases, and diarrhea in about 30%.  Biopsies are required to obtain a definitive diagnosis of GI lymphoma. Biopsy specimens can be obtained either by endoscopy, in which a long snake-like tube with a camera on the end is inserted in the cat’s mouth, and then advanced into the stomach and small intestine. Biopsies are obtained using special forceps that are inserted through the endoscope. Biopsy specimens can also be obtained via abdominal surgery. Both procedures require general anesthesia.

Once a diagnosis is achieved, the lymphoma is categorized into one of two general types: low grade (also called “small cell” or “lymphocytic”) or high grade (also called “large cell” or “lymphoblastic”). The type of lymphoma is significant in terms of prognosis. Low grade lymphoma has a significantly better prognosis than high grade lymphoma.

Chemotherapy is the treatment of choice, as lymphoma is the considered the most chemotherapy-responsive cancer. Combination chemotherapy, in which several drugs are administered sequentially is the primary method of treatment. In cases where the lymphoma causes a complete or partial intestinal obstruction or an intestinal perforation, immediate surgery may be necessary, followed by chemotherapy.

The prognosis for gastrointestinal lymphoma varies, depending on type. The median survival time with chemotherapy for high-grade lymphoma is only 2.7 months. Cats with low-grade lymphoma fare much better. The average survival time is 18 to 24 months, and cats can survive even longer. 

The diagnostic tests required to obtain a diagnosis are expensive, but you cannot avoid doing them if you want a definitive diagnosis. Frankly, with your cat down to 5 pounds, I unsure of whether your cat would survive the anesthesia required to obtain the biopsies necessary to obtain a diagnosis.  If I were your vet, I would start your cat on therapy for presumed GI lymphoma, which is prednisolone and chlorambucil, and see if your cat responds. At this point, you have little to lose.

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