A Different Animal: Cancer in Pets and People

Girls' Club

Just as in women, breast (mammary gland) cancer is a commonly diagnosed cancer in dogs and cats—if you live in a region where spaying and neuteringis not part of a routine pet preventive health care program. Removal of a dog’s ovaries before her first heat cycle during a spay procedure dramatically decreases the occurrence of breast cancer. That is why one common recommendation from veterinarians is to spay your puppy at about 6 months. Spaying also reduces the occurrence of breast cancer in cats. Breast cancer is the most common tumor found in female dogs and the third most common cancer in cats. In humans, it is one of the top three cancers in women, but obviously, preventive measures differ. In humans, we normally use screening mammograms as an early detection tool.

Lymphoma: Not a Good Prognosis

In cats, one in three cancer diagnoses is lymphoma, a cancer of a portion of the immune system known as the lymph system. It is most often diagnosed in the feline gastrointestinal tract, but any organ can develop the cancer. Dogs, too, can develop lymphoma. For example, both of former President George W. Bush’s Scottish Terriers, Barney and Miss Beazley, died from the malignancy.


Despite the incurablenature of lymphoma in cats and dogs, chemotherapy is the mainstay of treatment. Chemotherapy can offer pets who are suffering from the disease animproved quality and quantity of life. The typical dog receiving chemotherapy for lymphoma lives an extra year, which is a long time in dog years. In comparison, some forms of human lymphoma are curable, while others are not.

On the Surface

Although skin cancer is common in both pets and people, how it manifests as a disease is different. I rarely see skin cancer in pets caused by overexposure to the sun. The most common skin cancer I see in my daily oncology practice is mast cell tumor (MCT), mostly in dogs and occasionally in cats. Physician oncologists, however, rarely see that tumor in their practices. Most humans have never heard of a mast cell, but nearly all of us have felt their negative effects, since those are the cells responsible for allergic reactions ranging from from those to bee stings to hay fever. A mast cell tumor in pets occurs in the skin or just below the skin and is one of the tumors pet owners can identify just by petting their animals.


Mast cell tumors may just be a bump in the skin that looks like any other benign fatty tumor, but more commonly they are pink to red and may be scabby. A simple in-office test known as a fine needle aspirate can help in the early identification of an MCT. A veterinary pathologist will evaluate the aspirate and, if necessary, recommend surgical removal of any mast cell tumor. Surgery is often all that is needed to cure your dog of the tumor, but in some severe forms, chemotherapy and radiation therapy are also needed to control the malignancy.

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