Signs & Symptoms of Colon Cancer in Dogs

Veterinarian-reviewed advice you can trust

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Changes in weight, appetite, and energy levels are all potential signs of colon cancer in dogs. This umbrella term is sometimes used to refer to various types of malignant tumors of the large intestine, rectum, or anus, with the most common being adenocarcinoma. Diarrhea, constipation, and vomiting also indicate that something is wrong with your pet's digestive system. The thought of adenocarcinoma or other intestinal tumors in dogs is certainly a frightening prospect, but keep in mind that there are many noncancerous causes of these symptoms, including inflammatory bowel disease. Always consider these warning signs seriously and take your dog to the veterinarian for a medical evaluation.


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What is adenocarcinoma in dogs?

Adenocarcinoma is a type of cancer that occurs in the epithelial tissue, or lining, of the intestinal tract.‌ Most of these tumors grow in the colon or rectum, though some occur in the anus, anal sacs, or small intestine. The medical word for abnormal growth of tissue is neoplasia.


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Intestinal tumors affect less than 10 percent of dogs, so chances are you won't have to worry about adenocarcinoma or similar carcinomas in your pup. Colorectal cancer is most common in older male dogs, although these types of cancer can affect dogs of any gender or age. Collies and German shepherds are thought to have a genetic predisposition to adenocarcinoma.


Types of intestinal tumors

There are several types of tumors that can appear in your dog's digestive tract. While many cases of intestinal cancer in canines are malignant, it is also possible for the tumors to be benign and have little risk of spreading. One example of a benign intestinal tumor is leiomyoma.


Adenocarcinoma and lymphoma are malignant tumors that cause large bowel cancer, including colon cancer. Dogs can develop smaller benign growths, polyps, or adenomas in the membrane at the end of the colon near the rectum. Even benign cancers can pose a deadly risk to your pet if their size or number obstructs normal digestive function.


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Colon cancer in dogs symptoms

Adenocarcinoma and other colorectal cancers are difficult to diagnose at home because the early symptoms are similar to a range of gastrointestinal disorders, such as inflammatory bowel disease or benign intestinal tumors, such as polyps and adenomas. Clinical signs of adenocarcinoma and other intestinal tumors include:


  • Diminished appetite
  • Weight loss
  • Lethargy
  • Vomiting
  • Frequent diarrhea
  • Bloody vomit or feces
  • Black or tarry feces
  • Urgent need to defecate with difficulty doing so (tenesmus)
  • Maroon-colored feces
  • Inflamed peritoneum (peritonitis)
  • Swollen stomach
  • Anemia


Bloody or frequent vomiting and changes in stool composition or color should raise a warning flag immediately, as cancer can cause internal blood loss and other life-threatening issues in your pet. Contact your veterinarian immediately if you notice any of these symptoms.


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Diagnosing adenocarcinoma in dogs

If your veterinarian believes adenocarcinoma or another kind of tumor may be the root of your pet's health issues, they will conduct a physical examination, including laboratory tests, to reach a definitive diagnosis, followed by a rectal examination, or colonoscopy (endoscopy). If your dog need specialized veterinary medicine, you may be referred to a doctor who practices oncology, or cancer medicine, for animals.


Your veterinarian may take blood tests to look for changes in internal chemistry, which can help them find the location and type of cancer cells. High levels of calcium in the blood are a sign of lymphoma and other cancers, while gastrointestinal lesions may reduce the amount of protein present. Your DVM will conduct a radiography (X-rays) or an abdominal ultrasound to take images of your dog's colon and small intestine. They will also take fine needle aspirations or biopsies. The lab provides a histopathology report, meaning what they saw under the microscope, on biopsy samples.

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Treatment of adenocarcinoma in dogs

Treatment options for colorectal cancers depend on the specific type of cancer and its severity. Lymphoma and adenocarcinoma have the potential to spread to your dog's lymph system, lungs, liver, and other internal organs. In cases where the cancer has spread, chemotherapy may be the only viable choice for treatment. Surgical removal (resection) can eliminate isolated growths in the intestinal tract, although the size and aggressiveness of the tumors impact the success rate.


Dogs who survive surgical removal or radiation therapy for adenocarcinoma can have a good shot at recovery. Unfortunately, the average survival time for pups with metastatic tumors is only a few months. Even if curing the disease is not a viable option, a DVM can provide medications to temporarily ease your pet's discomfort and help restore their digestive function.

The bottom line

Adenocarcinoma in dogs is a rare but serious type of cancer. Symptoms, which include gastrointestinal issues such as diminished appetite, weight loss, frequent vomiting, diarrhea, anemia, and bloody or tarry stool, can also be associated with less serious conditions, including benign intestinal tumors or inflammatory bowel disease. If your dog exhibits any symptoms of gastrointestinal distress, especially changes in stool color or texture or bloody vomit, call your DVM immediately. Although the prognosis for adenocarcinoma is generally not good, dogs can survive with the help of surgical removal of the tumor or radiation therapy.



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