There are two forms of cancer that are more likely to affect the colon in dogs. According to the University of Pennsylvania, lymphosarcoma, commonly known as lymphoma, is one of the three most commonly found cancers in dogs. Dogs of any age can develop lymphosarcoma but it is most commonly found in dogs between the ages of 6 and 9. The second common type of colon cancer found in dogs is adenocarcinoma.
Digestive Signs and Symptoms
Since lymphosarcomas affect blood cells, called lymphocytes, and the lymphoid tissues that are in the gastrointestinal tract and adenocarcinomas grow as tumours in the glands next to the rectum, blood discharged by the cancers may be present in the dog's stools. According to The Daily Puppy, a dog with colon cancer may also have unexplained diarrhoea. Constipation and nausea are other digestive disorders that can indicate the presence of colon cancer.
Changes in Water Consumption
Dogs with colon cancer drink increased amounts of water. You may hear your dog drinking out of the water bowl with more frequency and for a longer duration. Consequently, you may notice your dog needing to urinate more often. This symptom may indicate other illnesses.
Changes in Appetite
A dog that is sick from colon cancer often eats less. This may be due to pain experienced when eating, nausea or other factors stemming from colon cancer. This loss of appetite can lead to rapid and noticeable weight loss and should be brought to your veterinarian's attention.
Changes in Coat
One of the outward signs of colon cancer in dogs is hair loss. A skin rash may also be present.
Colon cancer can cause changes in your dog's attitude and behaviour. Pain from cancer can cause signs of aggression like growling or biting. He may also show signs of depression or lethargy.
Other Physical Signs and Symptoms
Dogs with colon cancer may show signs of abdominal swelling. You may notice that your dog's stomach feels tight. This is also a symptom of bloat, a serious illness that requires immediate veterinary treatment. Muscle weakness and fever are also common symptoms seen with colon cancer.
In suspected colon cancer cases, you veterinarian will check your dog for further signs of illness. She may do a physical exam to feel any tumours or masses in the dog's abdomen and note any signs of pain. Further tests, like X-rays, ultrasound, blood tests and aspirates, will likely be required.