Top 10 Warning Signs of Cancer in Pets

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In dogs, halitosis, or bad breath, can be a sign of oral cancer.

Oral Cancer

Signs of oral cancers include bad breath, blood in the saliva, decreased appetite, and difficulty in chewing or swallowing.


Many different tumors occur in the mouths of dogs and cats, but all have similar clinical signs. The most common in dogs is melanoma, while squamous cell carcinoma commonly occurs in cats.

Dogs with melanoma of the oral cavity may experience blood in the saliva, difficulty chewing and swallowing, or a decreased appetite. Dog owners frequently first notice heavy-duty hound halitosis, or bad breath. Cats with squamous cell carcinoma may exhibit similar signs. Because these tumors often block the tear ducts, a cat owner might also notice an increase in eye discharge in just one of their pet's eyes or a funny look to their cat’s face because of the facial swelling associated with these tumors.


There are many types of cancers that occur in the oral cavity in both dogs and cats, and some of them can be quite aggressive. Anytime you note the above signs, or a lump or bump in your pet’s mouth, you should consult your veterinarian.

Osteaosarcoma (Bone Cancer)

Possible signs: Lameness and reluctance to put weight on a particular leg; painful hard lump or swelling.


The most frequently diagnosed tumor of the bone in both dogs and cats is osteosarcoma, or bone cancer. The clinical signs of any bone tumor include lameness and reluctance to put weight on a particular leg because the tumor makes it painful to walk on. If the tumor occurs in just the right location, you may be able to feel a hard lump or swelling on the bone, although be advised that these lumps can be extremely painful to the touch. An X-ray and biopsy will be necessary to confirm the diagnosis.

Be an Observant Owner

Though I’ve covered some of the more common signs of the most prevalent cancers, the important message here is to realize that many types of cancer have similar signs. Some of these signs can also be indicative of serious diseases other than cancer. When you are interacting with your pet daily, look for the signs I have described. If you see something of concern, have your pet evaluated by your family veterinarian. Even something as nonspecific as a general loss of energy or an unwillingness to exercise can be a warning that something is wrong. Always remember that an early diagnosis can sometimes help improve the chances of treatment success, whether your pet has cancer or any other serious disease.


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