Fast Growing Tumors in Dogs

By Christie Gross

Mast cell tumors (MCTs) are fast growing tumors found in dogs. They appear as raised hard lumps underneath the dog's skin. MCTs are a form of skin cancer. These tumors generally don't spread to other organs, although when it infects the lymph nodes the outcome is often fatal. MCTs are diagnosed in grades and stages based on the number of cell divisions and degree of spreading. Tumors of higher grades and stages (fast growing) unfortunately are given the worst prognosis.

Mast Cells

Mast cells are found in a dog's body. They release enzymes when stimulated by the immune system to ward off infection and irritants. When abnormal mast cells release too many enzymes, it creates a toxic reaction that results in a tumor as well as other problems, such as gastric ulcers, internal bleeding and an allergic manifestation.


The Bernese Mountain Dog Club of America reports 25 percent of canine skin tumors are MCTs. About 50 percent are malignant (fast growing). Most are found on the skin in the dog's legs or face, but they also can be found in the dog's spleen, liver and bone marrow.


According to Kate Connick's Courteous Canines, LLC---a canine information website---little is known about the cause of MCTs in canines. Although MCTs are more prevalent in older dogs, tumors don't discriminate and can affect dogs of various ages, gender and breed. Connick claims the average age of dogs with MCTs is eight or nine years old.


A dog owner usually is the first person to spot the tumor when he pets the dog and detects a lump on its body, prompting a visit to the veterinarian. The veterinarian takes a biopsy of the lump or removes it entirely and sends it a lab for analysis. A blood test also may be done to check for an elevated white count---an indication of a more serious infection. The lab analysis provides a grade and stage of the tumor.


Regrettably, the prognosis for a dog diagnosed with a fast growing tumor is terminal. Depending on the exact grade and stage of the cancer, tumors may be surgically removed to prolong the dog's life. Additional tissue is usually removed from around the tumor to ensure abnormal cells are eradicated. In certain cases, the dog's entire limb may be removed.
The dog is usually given drug therapy of prednisone and/or chemotherapy to reduce the tumor size and prevent rapid mastication. The dog is given pain medication to keep it comfortable and to maintain the best quality of life possible in his final weeks or months.