4 pet tumors, 10 symptoms and 5 risk reducers

Analysis by Dr. Karen Shaw Becker

top ten signs of tumors in pets

Story at-a-glance -

  • More dogs and cats, including younger pets, are being diagnosed with cancer today
  • Common types of cancer in dogs and cats include lymphoma and mast cell tumors
  • Cancer symptoms in pets are also seen in many other disorders and require prompt veterinary attention
  • There are steps every pet guardian can take to help reduce their animal companion’s risk of developing cancer

Sadly, as I write this, we’re seeing cancer in more pets — including younger dogs and cats — than ever before in our history. According to the American Veterinary Medical Association (AVMA), approximately 1 in 4 dogs will develop neoplasia at some point in their lives, and almost half of dogs over the age of 10 will develop cancer.1

There isn’t as much data available on cancer rates in cats, but we do know that certain cancers, for example, lymphoma, are more common in kitties than in dogs.

When discussing cancer in animal companions, it’s helpful to understand the meaning of certain commonly used medical terms. Neoplasia is the medical term used to describe uncontrolled, abnormal growth of cells or tissues in the body; neoplasm describes the abnormal growth itself. Neoplasms can be benign or malignant.

Benign neoplasms often grow slowly and may displace, but don’t usually invade surrounding body tissues, nor do they spread to other parts of the body. Malignant neoplasms behave less predictably, grow at various rates (including very rapidly), invade surrounding tissues and spread (metastasize) to other parts of the body.

Other related terms include tumor and mass, both of which are used to describe the physical appearance of a neoplasm. The word cancer is often used in place of neoplasia; however, only malignant neoplasms are technically cancers.

Common types of cancer in pets

Mammary gland cancer — Mammary gland or breast cancer is common in both dogs and cats. It’s the most common tumor found in female dogs and the third most common in cats.

One of the presumed and much-touted benefits of early spaying of female pets is a decreased risk of mammary gland cancer. However, a study published in 2012 in the Journal of Small Animal Practice found that insufficient evidence exists that spaying at any age reduces the risk of mammary cancer.2

Lymphoma — Lymphoma is an incurable cancer of the lymph system, which is part of the immune system. In cats, 1 in 3 cancer diagnoses is lymphoma, most often of the gastrointestinal (GI) tract. Dogs also develop lymphoma. To avoid contributing to your dog’s or cat’s lymphoma risk, make sure your pet isn’t exposed to cigarette smoke or lawn chemicals, especially those applied by professional lawn care companies.

Mast cell tumors — The most common type of skin cancer in pets is mast cell tumor (MCT). MCT is much more prevalent in dogs than in cats. In cats, mast cell tumors are most often seen in the skin of the head or neck, but they can occur anywhere in the body. Cats with these tumors are usually middle-age or older.

Unfortunately, kitties with mast cell tumors on the inside of their bodies — typically in the GI tract or the spleen — carry a much poorer prognosis than tumors occurring on the skin.

In dogs, mast cell tumors are most often found on the trunk, limbs and in between the toes. Prognosis depends on the tumor location, the extent of the tumor, the grade and the type of treatment given. Mast cell tumors of the skin are very different in dogs than cats. Surgery to remove the tumor is less invasive in cats, and the prognosis for a full recovery is much better in cats than in dogs.

Mast cell tumors with generally poor prognosis are those on the muscle, around the mouth or in internal organs, in the bloodstream or bone marrow and ulcerated tumors. Mast cell tumors that cause GI ulceration or are large, fast-growing or recurring also carry a much poorer prognosis.

Osteosarcoma — Osteosarcoma is an aggressive bone cancer that most commonly invades the long bones of large and giant breed dogs. Even with amputation of the affected limb and chemotherapy, which is the current standard of treatment, the average survival rate is only about a year.

10 symptoms of cancer in dogs and cats

Pets can develop neoplasia almost anywhere in the body, which is why the symptoms vary depending on the tissues and organs involved and the severity of the neoplasia. Make an appointment with your veterinarian if your pet displays one or more of the following 10 warning signs of cancer in pets:3

  1. Unusual swellings that don't go away or that grow — The best way to discover lumps, bumps or swelling on your dog or cat is to pet him.
  2. Sores that won't heal — Non-healing sores can be a sign of infection or cancer and should be evaluated by your veterinarian.
  3. Weight loss — Illness could be the reason your pet is losing weight but isn't on a diet.
  4. Loss of appetite — Reluctance or refusal to eat is another sign of possible illness.
  5. Bleeding or discharge — Bleeding can occur for a number of reasons, most of which signal a problem. Unexplained vomiting and diarrhea are considered abnormal discharges, as well.
  6. Offensive smell — An unpleasant odor is a common sign of tumors of the anus, mouth or nose.
  7. Difficulty eating or swallowing — This is a common sign of cancers of the mouth or neck.
  8. Reluctance to exercise or low energy level — This is often one of the first signs that a pet is not feeling well.
  9. Persistent lameness — There can be many causes of lameness, including nerve, muscle or bone cancer.
  10. Difficulty breathing, urinating or defecating — These symptoms should be evaluated by your veterinarian as soon as possible.

Many of these symptoms also occur with other disorders and diseases, but regardless, a pet showing any of these signs needs prompt veterinary attention. As with any disease, the earlier your dog or cat is diagnosed, the better the chances of a positive outcome.

Steps you can take to help reduce your pet’s cancer risk

1. Don't allow your dog or cat to become overweight — Studies show that restricting the number of calories an animal eats prevents and/or delays the progression of tumor development across species. Fewer calories cause the cells of the body to block tumor growth, whereas too many calories can lead to obesity, and obesity is closely linked to increased cancer risk in humans.

There is a connection between too much glucose, increased insulin sensitivity, inflammation and oxidative stress — all factors in obesity — and cancer. It's important to remember that fat doesn't just sit on your pet's body harmlessly. It produces inflammation that can promote tumor development.

2. Feed an anti-inflammatory diet — Anything that creates or promotes inflammation in the body increases the risk for cancer. Current research suggests cancer is actually a chronic inflammatory disease, fueled by carbohydrates. The inflammatory process creates an environment in which abnormal cells proliferate.

Cancer cells require the glucose in carbohydrates to grow and multiply, so you want to eliminate that cancer energy source. Carbs to remove from your pet's diet include processed grains, fruits with fructose and starchy vegetables like potatoes.

Keep in mind that all dry pet food (“fast food”) contains some form of potentially carcinogenic, highly processed starch. It may be grain-free, but it can't be starch-free because it's not possible to manufacture kibble without using some type of starch. The correlation between consuming fast foods and cancer has been established in humans,4 and my advice is to incorporate as much fresh, unprocessed food into your entire family’s diet as you can afford.

Cancer cells generally can't use dietary fats for energy, so high amounts of good-quality fats are nutritionally beneficial for dogs fighting cancer, along with a reduced amount of protein and no carbs.

Another major contributor to inflammatory conditions is a diet too high in omega-6 fatty acids and too low in omega-3s. Omega-6s increase inflammation while the omega-3s do the reverse. Processed pet food is typically loaded with omega-6 fatty acids and deficient in omega-3s.

A healthy diet for your pet — one that is anti-inflammatory and anti-cancer — consists of real, whole foods, preferably raw. It should include high-quality protein, including muscle meat, organs and bone. It should also include high amounts of animal fat, high levels of EPA and DHA (omega-3 fatty acids), and a few fresh cut, low glycemic veggies. This species-appropriate diet is high in moisture content and contains no grains or starches.

I also recommend making sure the diet is balanced following the ancestral diet recommendations, which have much more rigorous standards (higher amounts of minerals and vitamins) than our current dietary recommendations for pets (AAFCO). A few beneficial supplements like probiotics, medicinal mushrooms, digestive enzymes and super green foods can also be very beneficial to enhance immune function.

3. Reduce or eliminate your pet's exposure to toxins — These include chemical pesticides like flea and tick preventives, lawn chemicals (weed killers, herbicides, etc.), tobacco smoke, flame retardants, household cleaner and air scenting products like candles and plug-ins.

Because we live in a toxic world and avoiding all chemical exposure is nearly impossible, I also suggest offering a periodic detoxification protocol to your pet.

4. If your pet is a dog, especially a large or giant breed, hold off neutering or spaying until the age of 18 months to 2 years — Studies have linked spaying and neutering to increasing cancer rates in dogs. Even better, investigate alternative ways to sterilize your pet without upsetting his or her important hormone balance.

5. Refuse unnecessary vaccinations — Vaccine protocols should be tailored to minimize risk and maximize protection, taking into account the breed, background, nutritional status, lifestyle and overall vitality of the pet. We know vaccines can cause cancer5 and we know titer testing is a responsible way to ensure your pet has adequate immunity in place of over-vaccinating on an annual basis.