Identifying Signs of Cancer in Your Pet

National Pet Cancer Awareness Month

Dr. Thomas Edling, DVM, MSpVM, MPH, Petland’s consulting veterinarian.

I have found when talking with people there are many misconceptions about cancer. Cancer is not a specific disease like distemper or parvo, but hundreds of different related diseases each unique to the animal or person it is attacking.

Cancer is a collection of diseases in which some of the body’s cells begin to divide without stopping and spread into surrounding tissues. It can start almost anywhere in the body. Normally, cells grow and divide to form new cells as the body needs them. When cancer develops, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and form growths called tumors.

Two Main Types of Cancer

Solid tumors, which are masses of tissue and cancers of the blood, such as leukemias. Cancerous tumors are malignant, meaning they spread into, or invade, nearby tissues. In addition, some cancer cells can metastasize or break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.

So… what causes cancer?

Cancer is caused by changes to genes that control the way our cells function, especially how they grow and divide. These genetic changes can be inherited or arise during an animal’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the infections (bacterial and viral), chemicals, tobacco smoke, and ultraviolet rays from the sun.

Many forms of cancer that affect animals are very similar to those that attack people. Cancer is more common in older pets.

The Animal Cancer Foundation  has developed these 10 early warning signs for detecting cancer in your pet at the initial stages when treatment is the most effective. 

  1. Oral Odor

Oral tumors occur in pets and can cause a pet to change its food preference (i.e. from hard to soft foods) or cause a pet to change the way he/she chews their food.  Often, a foul odor can be detected in pets with oral tumors.

  1. Straining to Urinate

Difficulty urinating and blood in the urine usually indicate a urinary tract infection, however, if the straining and bleeding do not resolve rapidly with antibiotics or are recurrent, cancer of the bladder may be the underlying cause.

  1. Lameness

Unexplained lameness (especially in large or giant breed dogs) is a very common sign of bone cancer.

  1. Cough

A dry, non-productive cough in an older pet should prompt chest radiographs to be taken. This type of cough is the most common sign of lung cancer.

  1. Unexplained Bleeding

Bleeding from the mouth, nose, gums or blood in the urine or stool, that is not due to trauma should be examined. Although bleeding disorders do occur in pets, they usually are discovered at a younger age.

  1. Chronic Vomiting or Diarrhea

Unexplained vom­iting or diarrhea should prompt further investiga­tion. Tumors of the gastrointestinal tract can often cause chronic vomiting and/or diarrhea.

  1. Chronic Weight Loss

When a pet is losing weight and you have not put your pet on a diet, you should have your pet checked. This sign is not diag­nostic for cancer but can indicate an issue.

  1. Abdominal Distension

When the “stomach” or belly becomes enlarged rapidly, this may suggest a mass or tumor in the abdomen or indicate internal bleeding.

  1. An Enlarging or Changing Lump

Any lump on a pet that is rapidly growing or changing in texture or shape should have a biopsy.

  1. Swollen Lymph Nodes

These “glands” are located all throughout the body but are most easily detect­ed under the jaw or behind the knee. When lymph nodes are enlarged, they can suggest a common form of cancer called lymphoma.

Remember, many of these symptoms do not diagnose cancer. If your pet has diarrhea or vomits, don’t jump to any conclusions.

Testing for Cancer

I am frequently asked by loving and concerned pet owners if there is a test for cancer in their pet. Because cancer is not a single disease there is no single blood test, or any other test will detect all cancers in your pet’s body. It is important to detect abnormalities or changes in your pet early and work with your veterinarian to determine the cause.

Hopefully your pet will never experience cancer, but if it does here are some very important nutrition tips that were developed by the Animal Cancer Foundation

If your pet is at a healthy weight when diagnosed with cancer, don’t make changes to the dietary routine.

If your pet is obese when diagnosed with cancer, discuss with your veterinary professional team the best method to get to an ideal weight. Why? Although obesity has not yet been linked to increased cancer risk in dogs or cats, obesity has been linked to cancer in people, so it’s a likely risk factor for pets. too.

In 2012, Tufts University’s Clinical Nutrition Service team composed of Cailin R. Heinze, DVM, MS, DACVN, Frank C. Gomez, BS, and Lisa M. Freeman, DVM, PhD, DACVN evaluated 27 “cancer diets” recommended for dogs with cancer, sourced from the internet and/or books, only to find that NONE met the minimum nutrition requirements mandated for commercial diets. (https://avmajournals.avma.org/doi/abs/10.2460/javma.241.11.1453)

Contrary to some claims that diet can prevent cancer in pets, Dr. Lisa Weeth, a board-certified veterinary nutritionist and author of the Weeth Nutrition blog, writes, “No dietary change or nutritional supplement has been definitively shown to prevent cancer in dogs or cats.” https://weethnutrition.wordpress.com/2015/05/25/nutrition-and-cancer-what-we-can-and-cant-do/

According to Dr. Lisa Weeth, Weeth Nutrition Blog, “The most likely risk factors for cancer are genetics, viruses, environmental toxins, age and the neuter status of pets.”

Tufts University’s Clinical Nutrition Service team reminds pet caregivers to avoid raw-diets or treats that easily harbor food-borne illnesses such as rawhide bully sticks, freeze-dried treats, and similar products, because pets with cancer are immune-compromised and more susceptible to these infections.

Thinking about a home-cooked diet for your pet? Consult with a board-certified veterinary nutritionist before beginning a new program to be sure the plan is nutritionally sound.

A board-certified veterinary nutritionist will review your pet’s medical and diet history, evaluate the current diet, answer questions, and design a plan for you and your veterinarian to follow.

Good news: most commercial dog foods contain enough Omega-3s to support a pet’s nutrition and some evidence suggests Omega-3s have some benefit for pets with cancer.

Remember, most pets do NOT experience side effects from cancer treatment, but if they do a veterinary oncologist will prescribe medication to counter the effect.


I hope this article didn’t ruin you day and take your thoughts to bad places. Cancer is real and is something we must deal with in the lives of our pets. It is important to understand the basics of cancer and what to look for in your furry, feathered or scaly family member so you can catch it early when the chances of successfully treating the disease are the greatest. Cancer detection and treatment research has come a long way but still has far to go.

There are many outstanding organizations out there working hard to beat these diseases that could use your help.  Start a fundraiser or simply donate to the organization to help fund their research on these devastating diseases.

Meet Petland’s Consulting Veterinarian, Dr. Thomas Edling, DVM, MSpVM, MPH:
Dr. Edling received his BS in Industrial Engineering from Texas A&M University in 1981 and his degree in Veterinary Medicine (DVM) from Colorado State University. He previously served as Vice President of Veterinary Medicine for Petco and was on the faculty of the University of Wisconsin Veterinary Medical Teaching Hospital. In addition, Dr. Edling completed the American Board of Veterinary Practitioner’s residency program for Companion and Wild Avian Medicine and Surgery, at North Carolina State University, where he also received his Master in Specialized Veterinary Medicine (MSpVM) in 2001. In 2011, Dr. Edling completed the Master of Public Health (MPH) program at Johns Hopkins University. As a veterinarian, Dr. Edling works closely with the Pet Industry Joint Advisory Council (PIJAC), the Centers for Disease Control and Prevention (CDC) and the National Association of State Public Health Veterinarians (NASPHV).


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