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Gastrointestinal Cancer

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Cancer of the gastrointestinal (GI) system is relatively rare in pets. When it does occur, it is most common in the small intestine of cats, and in the large intestine and rectum of dogs, especially in Boxers, German Shepherds, Poodles, Great Danes, and spaniels.  In cats, intestinal cancer is often associated with FeLV infection. As with most cancers, GI tumors tend to occur in older (10+ years) pets.

The signs associated with GI cancer depend on the location of the tumor or tumors. Cancer of the stomach or initial portion of the small intestine often causes vomiting; the vomit may contain red blood or partially digested blood (which looks like coffee grounds). Cancer of the large bowel often shows up as diarrhea (also sometimes containing red blood or darker, digested blood) and straining to defecate. In some cases a tumor can completely block the GI tract, leading to severe tension and pain within the abdomen. Other more generalized signs include weight loss, loss of appetite, and lethargy.

Diagnosis begins with a thorough history and physical examination. Your veterinarian may be able to feel tumors of the small intestine by abdominal palpation. Similarly, rectal examination may reveal masses or irregularities within the colon that suggest cancer. Abdominal x-rays (including contrast radiography) and ultrasound are often used to localize and delineate abdominal masses. In some cases, exploratory surgery or endoscopic examination can be used to obtain biopsy specimens for microscopic evaluation. Other tests may include blood work and urinalysis.  All affected cats should be tested for FeLV.

Surgical removal is the treatment of choice for most GI cancers. Your vet will remove two to three inches or more of bowel on either side of the tumor, in an attempt to get all of the cancer. Samples of the tumor will be sent for microscopic examination, which will provide more specific information on the type of cancer and its long-term prognosis. Depending on the findings, your vet may suggest follow-up chemotherapy to address residual cancer. In cats with lymph cancer of the bowel, chemotherapy has prolonged life for an average of six months. 


What pets are most at risk of GI cancer?

Gastrointestinal cancer is relatively rare in pets, but it is most common in older dogs (especially Boxers, German Shepherds, Poodles, Great Danes, and spaniels) and in cats with FeLV infection.

How is GI cancer diagnosed?

Your vet may be able to feel an abdominal mass(es) on palpation, but most often x-rays or ultrasound are used to localize and delineate the tumor. A biopsy is needed to definitively identify the tumor type and to provide a prognosis. 

How is GI cancer treated?

Surgical removal is the preferred treatment, with follow-up chemotherapy in some cases.  Prognosis depends on whether or not all the cancer could be removed.

Credit: Written and reviewed by John A. Bukowski, DVM, MPH, PhD and Susan E. Aiello, DVM, ELS
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