Intestinal Tumours
These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout “What is Cancer”. If not already performed your veterinarian may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.
We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.
What are these tumours?
Tumours of the intestinal epithelial lining include non-cancerous polyps, benign adenomas and malignant epithelial tumours (adenocarcinomas). The polyps and adenomas may be multiple and cause local obstruction. The malignant tumours cause progressive illness and often spread (metastasize) before clinical diagnosis. Secondary tumours 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 tumours is often only months, although it is longer if the tumour has not spread before surgery.
What do we know about the cause?
The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances which come together for the unfortunate individual.
Cancer induction is a multistep process called tumour 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 animal 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 commoner in older animals.
Are these common tumours?
Intestinal tumours are uncommon in dogs. The average age of affected dogs is 9 years. The majority (60%) of the tumours are in the lower bowel, the colon and rectum.
"Intestinal tumours are uncommon in dogs."
In cats, the tumours are rarer than in dogs but male cats and Siamese breeds are more at risk. The age range is 2-17 years. They are usually in the small intestine with most occurring at the junction with the large bowel.
How will these cancers affect my pet?
The usual clinical signs are weight loss, loss of appetite, vomiting, diarrhoea and blood in vomit or faeces. Vomiting tends to occur more with tumours in the upper (small) intestine and diarrhoea with tumours of the lower (large) intestine. Constipation is sometimes a sign rather than diarrhoea and an abdominal lump may sometimes be felt by your veterinarian. There may be swelling of the abdomen with fluid (ascites) and fluid in the tissues under the skin (oedema) because the blood protein concentration is low.
How are these cancers diagnosed?
Cancer is often suspected from the clinical signs. Radiography (x-rays) may be useful in detecting the tumours. Blood tests are not diagnostic but sometimes indicate if the tumour is bleeding internally. In order to identify the tumour, it is necessary to obtain a sample of the tumour 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 tumours 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 specialised laboratory where the slides are examined by a veterinary pathologist.
What types of treatment are available?
Treatment is surgical removal of the tumour.
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, tumours 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 pet?
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 pet can pass urine and faeces or to give treatment to aid this.
If you require additional advice on post-surgical care, please ask.
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?
“Cure” has to be a guarded term in dealing with any cancer.
Adequate surgical removal of polyps and benign tumours of the rectum and colon usually results in recovery but many are multiple so further tumours grow. In people, larger tumours recur more commonly and become malignant more frequently. Microscopic grading and staging of the tumour helps to indicate the probability of recurrence.
Surgery is not curative for intestinal tumours 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 tumours 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 tumours and are not transmitted from pet to pet or from pets to people.
Adapted by Philip H Brain, BVSc, CMAVA, FACVSc (small animal medicine), FAVA © Copyright 2015 LifeLearn Inc. Used and/or modified with permission under license.