Why am I seeing so much gastrointestinal cancer (and cancer in general) in cats?

Gastrointestinal cancer can strike cats of any age, although it is mostly seen in older cats. The gastrointestinal tract is susceptible to several types of cancer, however, lymphoma is the most common. Exactly why lymphoma develops in some cats is not clear, but viruses may play a role.

The feline immunodeficiency virus (FIV) is associated with an increased risk of lymphoma. Cats infected with FIV are 5.6 times more likely to develop lymphoma compared to FIV-negative cats. Infection with the feline leukemia virus (FeLV) dramatically increases the risk of developing lymphoma; FeLV-positive cats are 62 times more likely to develop lymphoma than their negative counterparts. Most cats that develop gastrointestinal lymphoma, however, are negative for these two viruses.

Gastrointestinal lymphoma 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. 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 a special forceps that is 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 is causing 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. Median survival of 18 - 24 months has been reported, and it is not uncommon for cats to survive even longer.

As the year 2009 came to a close, I looked over our hospital statistics. In 2009, we performed 37 gastrointestinal endoscopies. Twenty cats were diagnosed with inflammatory bowel disease. One cat was diagnosed as normal. Sixteen cats had lymphoma. That’s almost one case of gastrointestinal cancer every three weeks! Our hospital opened in January 2003. It took us 38 months to diagnose our first 16 cases of lymphoma. None of the cats diagnosed with GI lymphoma were FeLV or FIV positive. 15 of the 16 were low grade. A recent article in the Journal of Feline Medicine and Surgery gave a survival time of 19 months for cats with low grade gastrointestinal lymphoma. A chapter in the newly released textbook “Consultations in Feline Internal Medicine” gave an even better prognosis: 25 months! I haven’t calculated the survival times of our hospital’s patients, but I can say that most of them have done very well on chemotherapy. We’ve seen some pretty long-term survivors. “Pez” lived about 24 months. “Julie” is still alive at 30 months after the diagnosis. (Pez would have lived longer. He died of old age. He was 19. He was still in remission when he died.)

Exactly why we’re seeing so much gastrointestinal lymphoma is a mystery. If there’s any consolation in all of this, it’s the prolonged survival with treatment. Trust me, there are much worse cancers to have than low-grade gastrointestinal lymphoma. Unfortunately, I’m seeing an increase in all types of cancers, including some pretty odd ones. We’re not even a month into 2010 and I’ve already diagnosed a biliary carcinoma (no treatment possible), an extraskeletal osteosarcoma (first one we’ve seen since we opened in 2003; no treatment except to amputate the leg), and a B-cell lymphoma of the bone marrow (a rare, bizarre cancer; we’re attempting to treat with chemotherapy).

I can think of two reasons why we’re seeing an uptick in cancer. One reason is that cats are living longer than ever before, and are now living long enough to develop these weird cancers that they would never have developed if they had died at age 13 or 14. Another reason is that we’ve gotten so much more sophisticated in our diagnostics that we’re able to detect cancers that had eluded us before. I guess this is the unfortunate price we pay for increased feline longevity. In any event, early detection is always the key to better survival, and with our hospital’s updated Wellness Plans and our emphasis on examining cats every six months (“Twice a Year for Life”), we’re one step ahead of the pack, I think, when it comes to cancer.