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Common Signs of Cancer: Part 1

By Stephanie Correa, DVM, DACVIM, Board-Certified in Medical Oncology, Founder and President of Animal Cancer Care Clinic

Pet owners want to understand and be aware of any possible signs and causes of cancer. Below are a few behaviors to monitor. When in doubt, always consult with your primary care veterinarian regarding any changes in behavior or physical appearance.

Early Warning Signs and Symptoms of Cancer

Monitoring your pet’s appetite is an important way to determine if your pet is ill. Changes in the appetite can be the first sign that there is something wrong. Appetite changes can occur for numerous reasons. Tumors in the mouth or stomach can make it difficult for a pet to chew or swallow. Cancer in the liver or kidneys can interfere with the function of these organs and make the pet feel nauseated so that there is no appetite present. If the appetite decreases or subsides without notice, weight loss will occur. Once a pet is losing weight from an undiagnosed disease, that could mean the disease has progressed, and treatment becomes more challenging.  Appetite is an early warning sign that can be monitored. Pay attention to your pet’s appetite daily by watching the food bowl to determine if the normal amount of food is consumed.

Monitoring the overall activity level is another way to determine the overall health of your pet. If a normally active and engaged pet becomes slow, lethargic, reluctant to exercise, or seems tired, that behavior could be a sign of cancer of the bone or cardiovascular system. Cancers of the bone are painful and patients with this type of cancer are reluctant to move due to discomfort. They may limp or have difficulty running or jumping. Cancers of the cardiovascular system can prevent the lungs and heart from functioning normally and pets will have exercise intolerance. Anemia is also a common finding in pets with cancer. Like people, pets that become anemic, or have a low red blood cell count, feel tired. They are not able to carry enough oxygen to their tissues and seem weak. Changes in activity level can occur slowly over weeks to months and may be more difficult to detect. Try to compare the activity level of the pet over the current month to the activity level of the pet two to three months earlier.  Sometimes these types of comparisons make it easier to realize that there has been a change. Sudden changes in activity level are easier to notice and often require immediate intervention. 

Changes in bowel or bladder habits can also indicate a disease process. In cats, gastrointestinal lymphosarcoma is a common type of cancer, which causes diarrhea. Both dogs and cats can develop bladder cancer, often indicated by blood in the urine or straining to urinate. Straining to have a bowel movement or blood in the stool can be early warning signs of colon or anal sac cancer. Start by observing changes in bowel habits during daily walks. Scooping your cat’s litter box on a daily basis is also a great way to watch for bowel changes in feline patients. Identifying these changes early is critical. 

Unexplained vomiting that does not resolve is another possible warning sign. Vomiting that occurs when something out of the ordinary is ingested is usually fine. However, when the vomiting continues for longer than a day or continues intermittently with no apparent reason, this is generally an indication that there is a disease process occurring. Many different types of cancer will cause vomiting.

Coughing or difficulty breathing is another symptom that can occur when cancer is present. Lung cancer occurs in dogs and cats, just as it does in people.  One of the first common warning signs is coughing. If a pet has a cough that continues over a period of weeks and does not seem to be getting better, please consult your veterinarian. Part 2 will include additional signs of possible disease progression.