Responsible pet owners know young and adult animals need a yearly checkup by a veterinarian. They may also realize senior pets should see a vet twice a year. But owners can’t depend only on checkups to catch problems: They need to look for changes in pets’ bodies and behaviors. Some diseases require immediate attention. And knowing the warning signs of cancer in pets may make a significant difference in treatment options and prognosis for survival.

Doctors diagnose more than 10 million new cases of cancer each year in dogs and cats across the United States, and cancer remains the leading cause of death in middle-aged pets. Animals age at a faster rate than humans, so a year in your life equals several years in theirs. That’s why early detection remains crucial.

Nine Possible Warning Signs of Cancer in Pets

These break down into three categories: Obvious physical changes, ranging from lumps to bleeding; subtler changes in the body; and behavioral changes related to diet, exercise and other habits. Whether or not these indicate cancer, you’ll want a vet to help you pin down the cause of any abnormalities.

Major Physical Changes

Swellings that persist or continue to grow over a few weeks’ duration could be indications of a tumor, from a bump on the leg (especially if your pet is lame there) to swollen lymph nodes around the jaw, shoulder, armpits or behind the legs. Run your hands regularly all around your pets to check for irregularities. They’ll appreciate the attention.

A discharge or open wound that won’t heal could be a sign of infection or cancer. Blood, pus, vomit, diarrhea or other abnormal excretions should be checked immediately by a veterinarian. Oral cancer can make gums bleed, while colon or rectal cancer can cause blood in stools. Be aware that skin tumors may initially be misdiagnosed as infections./We generally associate limping or other evidence of persistent pain with arthritis or muscular injury, but those can also be signs of cancer. Your vet may recommend an X-ray to rule out bone cancer, especially if you’ve noticed a lump that doesn’t get smaller on a limb.

Subtler Physical Changes

For all the jokes about “dog breath,” offensive odors from mouths, ears or other parts of the body should be checked out, especially if they smell different to you. Foul odors can be tipoffs to tumors in the mouth, nose, or anus. Not all pets with oral cancer exhibit pain or have trouble eating, so be wary of unfamiliar odors.

Constant coughing and difficulty breathing more often indicate problems in the heart and lungs, but they can be cancer-related: A tumor near the esophagus, nose or lungs can block airways, or cancer can spread to the lungs. Dogs with lymphoma may have coughing or noisy breathing because of enlarged lymph nodes in the throat.

Changes in urination and defecation may not be obvious but keep an eye out. Causes can be as mild as a urinary tract infection or as severe as a tumor in that tract or a mass near the anus. Imaging tests help vets figure out the cause.

Behavioral Changes

These can be difficult to track, especially in cats; they mask weakness and discomfort well. If your pet suddenly drops food or becomes a messy eater, a tumor in the mouth or neck may be putting pressure on the area, so it’s difficult eat or drink normally.

Diminished appetite can be a normal sign of aging, as in humans, but animals never stop eating without a cause. If your pet isn’t on a diet and loses weight, find out why. Anorexia and weight loss are the most common indicators of severe illness in cats. Chronic vomiting or diarrhea may also be signs, though dietary change, stress or unsuitable foods can induce those symptoms.
If a dog or cat seems weak, lethargic, intolerant of exercise or simply less interested in things he typically loves to do, something’s wrong. These may or may not be warning signs of cancer in pets, but a diagnosis by your veterinarian will point you in the right direction.

Think of CARE as the animal version of a medical center for humans. It provides all forms of treatment for pets through emergency care 24 hours a day and 365 days a year. It also offers board-certified specialty care, after you get a referral from your primary veterinarian. You’ll find a visual tour of the practice at

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