Tumors of the intestinal epithelial lining include non-cancerous polyps, benign adenomas and malignant epithelial tumors (adenocarcinomas). The polyps and adenomas may be multiple and cause local obstruction. The malignant tumors cause progressive illness and often spread (metastasize) before clinical diagnosis. Secondary tumors are found in the lymph nodes (glands), on the inside lining of the abdomen (peritoneum) and in the liver and lungs. Survival time with malignant intestinal tumors is often only months, although it is longer if the tumor has not spread before surgery.
What do we know about the cause?
The reason why a particular dog may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances that come together for the unfortunate individual.
Cancer induction is a multi-step process called tumor progression. Some cancers never progress past the first stages, so they remain benign. Others progress rapidly. It is probable that infections or certain chemicals are implicated in initiating or promoting this process but we do not have any specific knowledge of the causes.
Why has my dog developed this cancer?
Some animals have a greater tendency (genetic susceptibility) to cancer. Some breeds have far more cancers than others, often of specific types. The more divisions a cell undergoes, the more probable is a mutation so cancer is more common in older animals.
Are these common tumors?
Intestinal tumors are uncommon in dogs. The average age of affected dogs is 9 years. The majority (60%) of the tumors are in the lower bowel, the colon and rectum.
How will these cancers affect my dog?
The usual clinical signs are weight loss, loss of appetite, vomiting, diarrhea and blood in vomit or feces. Vomiting tends to occur more with tumors in the upper (small) intestine and diarrhea with tumors of the lower (large) intestine. Constipation is sometimes a sign rather than diarrhea and an abdominal lump may sometimes be felt by your veterinarian. There may be swelling of the abdomen with fluid (ascites) and fluid in and tissues under the skin (edema) because the blood protein concentration is low.
How are these cancers diagnosed?
Cancer is often suspected from the clinical signs. X-rays may be useful in detecting the tumors. Blood tests are not diagnostic but sometimes indicate if the tumor is bleeding internally. In order to identify the tumor, it is necessary to obtain a sample of the tumor itself. Various degrees of surgical sampling may be needed such as endoscopy and exploratory surgery. The tissue samples are submitted for microscopic examination. Biopsies taken with the aid of an endoscope are sometimes diagnostic for tumors of the rectum and colon but examination of a larger surgical specimen is often needed. The histopathology (microscopic examination of specially prepared and stained tissue sections) is done at a specialized laboratory where the slides are examined by a veterinary pathologist.
What types of treatment are available?
Treatment is surgical removal of the tumor.
Non-steroidal anti-inflammatory drugs (NSAIDs) can protect against colon cancer in people, possibly because they reduce the formation of compounds called prostaglandins. In one study in dogs, tumors in the rectum were reduced in size by treatment with suppositories of one of these drugs, piroxicam.
Can these cancers disappear without treatment?
Cancer rarely disappears without treatment but as development is a multi-step process, it may stop at a certain stage. The body’s own immune system can kill cancer cells but it is rarely 100% effective. Rarely, loss of blood supply to a cancer will make it die but the dead tissue will probably need surgical removal.
How can I nurse my dog?
After surgery, the operation site needs to be kept clean and your pet should not be allowed to interfere with it. Any loss of sutures or significant swelling or bleeding should be reported to your veterinarian
Your pet may require a special diet and you may be asked to check that your dog can pass urine and feces or to give treatment to aid this.
How will I know how the cancer will behave?
Histopathology will give your veterinarian the diagnosis that helps to indicate how it is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread).
When will I know if the cancer is permanently cured?
’Cured’ has to be a guarded term in dealing with any cancer.
Adequate surgical removal of polyps and benign tumors of the rectum and colon usually results in recovery but many are multiple so further tumors grow. In people, larger tumors recur more commonly and become malignant more frequently. Microscopic grading and staging of the tumor helps to indicate the probability of recurrence.
Surgery is not curative for intestinal tumors with microscopic evidence of spread at the time of surgery. The median survival time for these dogs is approximately three months. The median survival time without microscopic evidence of spread at the time of surgery is approximately 15 months. In order to make this microscopic assessment, your veterinarian has to submit a lymph node (gland) for histopathology.
The efficacy of other treatments has not been fully assessed but, in people, there is little convincing evidence to indicate additional therapy improves survival time.
The great majority (90%) of intestinal tumors in cats are malignant. Most will have metastasized (spread) by the time of diagnosis. Average survival time is 15 months with a range of two days to two years.
Are there any risks to my family or other pets?
No, these are not infectious tumors and are not transmitted from pet to pet or from pets to people.
Based on material written by Joan Rest, BVSc, PhD, MRCPath, MRCVS. and modified with permission from Lifelearn Inc.
© Copyright 2004 Lifelearn Inc.
