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Dear Daisy Dog

Our veterinarian removed a skin lump from Connor, our 8-year-old golden retriever. The biopsy report called it a “mast cell tumor, Grade II” and said the edges of the removed skin were free of tumor cells. What is the prognosis? Should we do chemotherapy?

Daisy Responds

Mast cell tumors (MCTs) are the most common skin cancers in dogs, though they are uncommon in other species.

Most MCT biopsies are reported to be Grade II, of intermediate severity between Grade I (not very serious) and Grade III (which recur locally and spread quickly to other parts of the body.)

Grade II MCTs, once completely removed, are not usually a problem. However, some act like Grade III MCTs.

The newest technique to determine which category Connor’s MCT falls into is a series of tissue marker tests. These tests add to the cost of the biopsy, but they provide additional information about the severity of a Grade II MCT.

If tissue marker information is not available, most oncologists feel that chemotherapy is not necessary once a Grade II MCT has been completely excised.

Other factors thought to play a role in the prognosis of MCTs are breed (they are especially aggressive in boxers) and tumor location (bad locations are the feet and around the rectum and prepuce.)

Dr. Seuss said it best: “One of these is not like the other. Don’t ask me why; go ask your mother.” He must have been thinking of Grade II mast cell tumors.

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