Pet Cancer: Can You Spot the Signs?

Medically Reviewed by Will Draper, DVM on July 21, 2016
3 min read

You know about the signs of cancer your doctor tells you to watch out for -- an irregular mole or a suspicious lump. But do you know the signs in your pets?

Not just a two-legged problem, cancer is all too common in cats and dogs. Veterinarians diagnose about 6 million cancers a year in dogs and another 6 million in cats.

"Animals can't tell us what they're feeling. We have to be observant," says Brian Collins, DVM, chief of community practice at Cornell University College of Veterinary Medicine in Ithaca, NY.

A lump isn't automatically cause for alarm. Middle-aged and older dogs often get benign fatty tumors. But a veterinarian should check any lump on your pet. If you've been watching one and it changes, that warrants a vet visit, too. "It may start to grow more rapidly, become [an open sore], start bleeding, or seem painful because the animal is licking or chewing it," Collins says.

A red, teary, or bulging eye might be harboring a tumor. Tumors can also cause symptoms of an ear infection. "The ear might be uncomfortable. The pet might be shaking its head or clawing at the ear. There might be discharge or an odor," Collins says.

Growths on the lips, gums, or tongue can be a sign of oral cancer. These may come with bad breath, too.

A suddenly expanded belly without any other weight gain could be a tumor. Unexplained weight loss could be a complication of cancer as well.

Cancer can cause changes in your pet's behavior or habits, such as less appetite, chronic vomiting or diarrhea, coughing or labored breathing, more thirst, and change in food preferences. Take notice if a once-active dog suddenly spends all his time lying around. Limping could be a sign of bone cancer. Straining to pee or other changes in pee patterns, such as more volume or frequency, might be a red flag, too.

"Your pet's personality might seem to change. Maybe they become more withdrawn, act more irritable, or hide. They might develop new quirky behaviors. These could be potential signs of a brain tumor," Collins says. Cancer-related personality changes could also include pacing, agitation, and wanting to go outside more. 

Before you see your vet, don't panic or jump to conclusions. The tricky thing about symptoms of cancer is that they can be signs of other problems, too. Straining to pee, for example, could be a urinary tract infection. A cough in a dog might mean heart disease; in a cat, asthma. Lots of thirst can stem from diabetes or kidney problems. Diarrhea and vomiting may suggest any one of a host of diseases.

"A lot of these symptoms overlap with other diseases as well, so I generally recommend if people see any of these signs to go to the vet," Collins says. "We don't want people to always be on the edge of their seats about cancer, but we don't want to let something go unnoticed or progress too far before action is taken either."

Ask your veterinarian these questions:

  • If my pet is older, how will treatment extend his overall survival?
  • How long will my pet have a good quality of life without and with treatment?
  • What will be the cost and time commitment of treatment?
  • Are most people glad they pursued treatment for this type of cancer?

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