There is a rule for this, and it fits in a sentence. Dr. Sue Ettinger, a veterinary oncologist, wrote it after missing a malignant tumor on a dog belonging to one of her own technicians: if a dog or cat has a mass the size of a pea, one centimeter, and it has been there one month, get it aspirated or biopsied. She calls it See Something, Do Something.
Her reason is the part owners need to hear. A harmless fatty lump and a mast cell tumor can look and feel the same. In her words: even an experienced cancer specialist like me cannot look at or feel a mass and know what it is. I am not a microscope.
A fine needle aspirate is a needle put into the lump to draw out some cells, which go on a slide and under a microscope. No anesthetic, a few minutes, and often an answer the same day or from the lab within days. Many lumps turn out to be benign, but the only way to know is to look at the cells.
The American College of Veterinary Surgeons says mast cell tumors are the most common skin tumor in dogs, 14 to 21 percent of all skin tumors diagnosed. They can look like anything, and they can change size from day to day depending on how inflamed they are, which is why a lump that comes and goes is not reassuring. Boxers and Boston terriers make up about half of all cases; pugs, bullmastiffs, cocker spaniels, bull terriers, Staffordshire terriers, fox terriers, Labrador and golden retrievers, beagles, schnauzers and weimaraners are also on the list.
The good news is in the same page: a needle aspirate diagnoses them accurately in almost all cases, surgery with a wide margin of healthy tissue is the preferred treatment, and the grade of the tumor, which the lab reports, is what the outlook depends on. Lower grades mean longer lives.
Read 18 September 2026.