If an older dog develops fatty deposits or tumors under the skin, what causes that? Should they be removed? If they are removed will they grow back? Is there a way to prevent them?
These fatty deposits or tumors are called lipomas. They are soft, moveable lumps or bumps that are located under the skin. Since these tumors are painless and do not cause outward skin changes such as hair loss or infection, lipomas are often not found until owners are petting or brushing their dog or cat.
A lipoma is a type of tumor made up of adipose tissue (fat). Almost all lipomas are benign, so they do not spread anywhere else in the body, and they are slow-growing. Rarely, some lipomas can become infiltrative, meaning they “invade” or grow into other tissues, such as muscle or bone. Or a lipoma may become so large that it interferes with normal body mobility. The infiltrative lipomas are most commonly seen on the extremities (limbs), but have been reported in other sites.
There is another type of fatty tumor, called a liposarcoma, which does have malignant characteristics. These tumors have the potential to spread elsewhere in the body. Luckily, liposarcomas are uncommon.
Lipomas are most commonly found in middle-aged to older dogs. Female dogs develop lipomas more frequently than male dogs, as do overweight dogs. Less often, an older cat, especially one that is overweight, can also develop lipomas. Breeds that are more likely to have lipomas include Labrador retrievers, cocker spaniels, poodles, dachshunds and terriers.
It is not known why certain animals develop lipomas. Therefore, there is no way to prevent them. We do know that once a dog or cat has a lipoma, it is more likely to develop more. But don’t just assume that every new bump is a lipoma. Each lump should be evaluated by a veterinarian to verify that it is a lipoma and not a different type of tumor or lesion.
The diagnosis of a lipoma can typically be done right in your veterinarian’s office while you wait. A small needle is used to aspirate (suck out) cells from the lump. These cells are then transferred to a slide and examined under the microscope. If the diagnosis is still uncertain, a biopsy may be necessary.
Surgery can be done to remove lipomas. However, many lipomas are only a cosmetic problem, so surgical removal is not necessary in these cases. Often careful monitoring for any change in size or character of the tumor is all that is needed.
However, if the lipoma is so large that it bothers your pet or interferes with movement, or if it is rapidly growing or causing other problems for your pet, surgical removal is typically recommended. If a lipoma is completely surgically removed, it will not grow back. But if some of the tumor cells are left behind, local recurrence is possible.
Lipomas are a common tumor found in dogs. Fortunately, they are typically more of a cosmetic concern than a medical problem. But remember that not every soft lump is a lipoma. So pay attention to any new lump and bump you find on your pet, and be sure to point it out to your veterinarian during your next visit.