Intestinal Cancer in Dogs and Cats
Like with other organ systems, tumors and cancer can also occur in the intestine, and the severity and symptoms usually depend on where the cancer is located. Intestinal cancer is the uncontrollable growth of abnormal cells and tissues anywhere along the intestine. All intestinal cancer cases in dogs and cats cause severe illnesses and often result in poor prognosis even with treatment. Keep reading to learn about symptoms to watch out for and what can be done to determine a diagnosis for your pet.
What breeds are at risk for developing intestinal cancer?
Intestinal cancer is fairly uncommon in dogs and cats and accounts for less than 10% of all cancer cases in these animals. It’s not fully understood how intestinal cancer develops, but it is considered to be a result of several risk factors that lead to the formation, growth, and proliferation of cancer cells along the intestinal tract.
Age is a common risk factor in intestinal cancer, and most cases are diagnosed in dogs and cats with a mean age of 10 years or older. Reports have also shown that male cats and dogs are at a higher risk of developing intestinal cancer compared to females.
Genetics and breed are also established risk factors for intestinal cancer development in both dogs and cats. In dogs, German Shepherds are reported to be highly predisposed to develop leiomyosarcomas while adenocarcinomas are overrepresented in breeds like Collies, Boxers, West Highland Terriers, Doberman Pinschers, Poodles, and Shar-Peis.
In cats, Siamese breeds are at a significantly higher risk of developing intestinal cancers compared to other cat breeds. They account for about 70% of adenocarcinoma cases in cats and are twice as likely to develop intestinal lymphomas than other breeds.
Chronic intestinal conditions such as Inflammatory Bowel Disease in both dogs and cats are also believed to be a risk factor for intestinal cancer development. Persistent inflammation can cause mutational changes in the intestinal cells which may result in cancer formation.
Symptoms of Intestinal Cancer in Dogs and Cats
Intestinal cancers in dogs and cats have a wide range of clinical signs, depending on the exact location of the cancer or tumor. Primary signs include vomiting, diarrhea, weakness, decrease in appetite, and weight loss. Often, the vomit can be undigested food, gastric acid, or blood, depending on where the cancer is located or if the tumor has started bleeding already.
Bleeding tumors, if uncontrolled, can cause anemia in affected dogs and cats and result in severe weakness or even death. Dogs and cats with cancer growth in the large intestine will often strain when having a bowel movement, as the tumor can cause partial or complete obstruction in the intestinal tract. Excessive straining can lead to rectal prolapse in both dogs and cats.
Intestinal cancers are at high risk of spreading to other organs and systems through metastasis. Common organs where intestinal cancers metastasize to are the lungs, kidneys, and liver. This often results in symptoms such as breathing difficulties, urination problems, and neurological symptoms like tremors and seizures depending on the organs affected.
Types of Intestinal Cancers Seen in Dogs and Cats
Intestinal cancers can be classified depending on where they’re located along the different segments of the intestine and the type of cell they originated from. In dogs, the most common intestinal cancers report are adenocarcinomas, leiomyosarcomas, and lymphomas. In cats, the most common intestinal cancer seen is lymphoma.
Intestinal adenocarcinomas are biologically active cancer cells that originate from the glandular epithelial lining of the intestinal wall. It is a highly invasive intestinal cancer that causes severe illness and a low chance of survival. Dogs and cats affected with this type of cancer often have a poor prognosis even with treatment. Treatment would often involve surgical removal of the tumor and chemotherapy.
Leiomyosarcomas are intestinal cancers that grow between the muscular layers of the intestine. Unlike adenocarcinomas, this type of cancer is less aggressive and has a relatively lower risk of metastasis. Most cases can go into remission for up to 30 months with just surgical excision alone.
Intestinal lymphomas are abnormal lymphoid cancer that grows in the intestine. The gastrointestinal tract, particularly the small intestine and the large intestine, have high concentrations of lymphoid tissues for protection against pathogens that the animal ingests. Lymphomas originate from these lymphoid tissues and cause severe clinical signs in affected dogs and cats.
Lymphomas are commonly treated with multi-drug chemotherapy, but animals that have diffuse and metastasized lymphoma don’t respond well to treatment and may succumb to cancer in an average of 3 months. Those with less diffuse lymphoma cases respond well to chemotherapy, with around 80% of the cases go into initial remission.
How is intestinal cancer diagnosed in dogs and cats?
Initial screening will often require a complete blood panel. This will give indications of possible ongoing inflammation, metastasis, and abnormal levels of lymphocytes (in cases of intestinal lymphoma). Diagnostic imaging such as contrast radiography (x-rays) and ultrasonography can help visualize the presence of tumors and growths if they’re large enough.
Endoscopy is the best method to visualize the presence of tumors along the intestinal wall. This involves inserting an instrument, called an endoscope, inside the intestinal lumen either via the mouth or the anus to get real-time visualization of the intestinal lining. However, this is only effective in intestinal cancers that grow on the epithelial lining (adenocarcinoma) and may not be able to properly visualize cancer tissues originating from the submucosal layers (lymphomas and leiomyosarcomas).
Definitive diagnosis is done through biopsy. Samples for biopsy can be taken either through endoscopy or surgical procedures like laparotomy. A biopsy allows for proper identification and staging of intestinal cancer which are important in deciding the ideal treatment regimen for the affected dog or cat.
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