Top 10 Warning Signs of Cancer in Pets

Cat on being weighed on scale
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Signs of lymphoma in cats can include weight loss, poor appetite, vomiting, diarrhea or blood in the stool.

Lymphoma

Possible signs: In cats, weight loss, poor appetite, vomiting, diarrhea or blood in the stool. In dogs, rapidly enlarging lymph nodes. Occasionally, increased water consumption and urine output.


The most common form of lymphoma differs between dogs and cats. In cats, insidious weight loss is the hallmark of lymphoma, which occurs most commonly in the feline gastrointestinal tract. I know from personal experience and from scientific research that pet owners sometimes have a hard time assessing a plumper-than-normal or a skinnier-than-usual dog or cat. Weight loss and appetite loss are indicative of many diseases other than cancer, though, so it’s important to notice any changes. Next time you visit your veterinarian, ask her to help you assess the “body condition score” of your pet. Ideal body conditions generally score about a three on a scale of one to five or a four or five on a scale of one to nine.

One good way to keep tabs on your pet’s weight is to stay in close contact with your veterinarian, who keeps detailed records about your pet’s weight as part of her wellness examinations. Most veterinary offices have a readily accessible scale and would welcome your pet for a quick weigh-in anytime you are concerned about potential weight loss. If lymphoma affects your cat’s stomach, you may see vomiting. If it affects her intestines, you may notice diarrhea or blood in the stool. Some cats with lymphoma may also have a poor appetite or stop eating altogether.


From my veterinary perspective, the most common clinical sign of lymphoma in dogs is swollen lymph nodes. The easiest lymph nodes for owners to see and feel are just beneath the skin under the chin, in front of the shoulders and behind the knees. In a normal, healthy dog, lymph nodes are not detectable by the average owner. Lymph nodes affected by lymphoma, however, are an example of rapidly enlarging lumps that should be immediately evaluated by a veterinarian. Another key sign, although it is seen in less than half of dogs with lymphoma, is a metabolic change that results in an increase in both water consumption and urine output. Again, keep in mind that increased drinking and urinating can also be signs of diseases other than cancer and always warrant a visit to your veterinarian.

Skin Cancer

Possible signs: Lumps or bumps that enlarge, sores that do not heal, limping and/or bleeding or broken toenails.


In dogs, the most common type of malignant skin cancer is a mast cell tumor. These tumors are superficial lumps that can be painful. They often swell, frequently bleed and then scab over, only to bleed again a few days later. They should not be squeezed by the owner, as squeezing can make them swell even more.

Similar signs occur in cats with the most common type of feline skin cancer — squamous cell carcinoma. This tumor may cause skin ulcers that bleed and scab, especially in the lightly haired skin around the eyes and nose and on the ear tips.


Unlike in humans, melanoma is typically benign in dogs and cats. It can occur in the mouth in dogs, however, and when it occurs in this location it is often highly malignant (see the Oral Cancers section below). The other location where melanoma can be malignant is at the junction between a dog’s claw and toe. If you see swelling, bleeding, an unexpected broken toenail or limping caused by a mass at the claw-toe junction, it may indicate a serious problem in your dog. Your dog should be evaluated by your veterinarian, who may recommend a biopsy.

Melanoma is somewhat unique among cancers in that it spans the spectrum from benign when found in the haired skin of pets to deadly when it occurs in the toes or mouths of dogs.


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