Lipomas are lumps of fatty tissue found just beneath the surface of the skin. They are common in dogs and occur occasionally in cats. Generally, lipomas tend to be round, soft, and movable, and are often spotted on dogs and cats by owners when petting or grooming their pets, since they do not cause any pain or inflammation.
Lipomas, or fatty tumors as they are often called, occur in just about all breeds of dogs of all ages, but tend to occur most commonly in middle aged to older: cocker spaniels, dachshunds, poodles, retrievers, and terriers. The exact cause for the formation of lipomas is not really known, but there appears to be a genetic connection, with multiple litter mates often developing these tumors. Also, once one lipoma arises in a dog or cat, that same patient is likely to get more of them, however, if new ones arise, owners should should have them checked by the vet to ensure that they are not malignant (cancerous) tumors.
Generally, lipomas do not get much bigger than the size of a golf ball, however, in a minority of lipoma cases in large breed dogs, retrievers in particular, the lipomas can get very large, some even as large as basketballs. Lipomas are benign (not cancerous) tumors, that are usually merely a cosmetic matter, not necessitating removal. Lipomas are most typically diagnosed by clinical examination and cytology (cellular analysis) of a fine needle aspirate of the suspected mass. Medically, veterinarians generally recommend surgical removal of lipomas only when they have become exceptionally large, and/or when they are in a location where they are causing obstruction to movement, eating, or drinking.
In rare cases, lipomas can become cancerous, causing inflammation around the tumor site, and may have the ability to metastasize (spread to other tissues) and are known as infiltrative lipomas. Lipomas of this kind are treated with a combination of surgery and radiation. Fortunately, however, infiltrative lipomas are rare in dogs, and exceedingly rare in cats.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 8/18/2012