Cancer in pets: The warning signs

Aug 24, 2012 at 6:03 p.m. ET

It’s been said that an "ounce of prevention is worth a pound of cure" -- this is true for our own health as well as our pets. But because they can't talk, we need to rely more on physical clues to detect cancer in the earliest stages in our dogs and cats.

Sick dog

The Animal Cancer Foundation (ACF) develops and supports research that advances the prevention and treatment of cancer for people and pets. Here, find 10 symptoms to help you spot warning signs in your pet.

10 Common signs of cancer in pets

There are 10 common warning signs that every pet owner should know. Now don’t panic: these are just potential warning signs and don't necessarily mean anything is seriously wrong. However, let these signs prompt you to visit to your veterinarian and know for sure.


Swollen lymph nodes

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


An enlarging
or changing lump

Any lump on a pet that is rapidly growing or changing in texture or shape should have a biopsy. Lumps belong in biopsy jars, not on pets.


Abdominal distension

When the “stomach” or belly becomes rapidly enlarged, this may suggest a mass or tumor in the abdomen or it may indicate some bleeding that is occurring in this area. A radiograph or an ultrasound of the abdomen can be very useful.


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 that something is wrong. Many cancer patients have weight loss.


Chronic vomiting or diarrhea

Unexplained vomiting or diarrhea should prompt further investigation. Often, tumors of the gastrointestinal tract can cause chronic vomiting and/or diarrhea. Radiographs, ultrasound examinations and endoscopy are useful diagnostic tools when this occurs.


Unexplained bleeding

Bleeding from the mouth, nose, penis, vagina or gums that is not due to trauma should be examined. Although bleeding disorders do occur in pets, they are usually discovered while pets are young. If unexplained bleeding starts when a pet is old, a thorough search should be undertaken.



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. Please remember there are many causes of cough in dogs and cats.



Unexplained lameness, especially in large- or giant-breed dogs, is a very common sign of bone cancer. Radiographs of the affected area are useful for detecting cancer of the bone.


Straining to urinate

Straining to urinate and blood in the urine usually indicate a common urinary tract infection; if the straining and bleeding are not rapidly controlled with antibiotics or are recurrent, cancer of the bladder may be the underlying cause. Cystoscopy or other techniques that allow a veterinarian to take a biopsy of the bladder are useful and sometimes necessary to establish a definitive diagnosis in these cases.


Oral odor

Oral tumors do 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 manner in which it chews its food. Many times a foul odor can be detected in pets with oral tumors. A thorough oral examination with radiographs or CT scan, necessitating sedation, is often necessary to determine the cause of the problem.

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