A Lipoma is a benign fatty lump. They are very common in middle-aged and older dogs. . Certain dog breeds may be at risk, including, but not limited to: Doberman Pinschers, Schnauzers (miniatures), Labrador Retrievers, and Beagles. They can also appear in cats and horses, but not as often.
Lipomas are usually just under the skin, but they can be infiltrative, meaning they have invaded into surrounding tissue such as muscle or connective tissue. These growths can appear anywhere on the body, but they are most frequently located on the belly (mid-chest and down) and upper legs.
Any and all lumps should be checked out by your veterinarian, regardless of how your pet is acting. Your vet will assess the location, duration, firmness, and size. A needle aspirate may also be taken to look at what type of cells make up the lump.
A fine needle aspiration (FNA) is when a sterile needle is inserted into the lump to collect cells from the growth. This is not painful, and not usually even noticed by most pets. The FNA is also used to detect histiocytoma in dogs. Your vet will then place the collected cells on a microscope slide, stain them, and take a look under the microscope.
Should a Lipoma Be Surgically Removed?
Provided your veterinarian has performed a needle aspirate and is certain that it is indeed a lipoma, most vets recommend a watch-and-wait approach. The lump should be checked at regular intervals, to make sure there haven't been any cellular changes. Large lumps, especially those under a limb or in another location that could interfere with movement or function, should be removed as soon as possible.
Check All New Lumps
If a new lump has appeared on your pet, it could be another benign lipoma. Dogs that form lipomas are prone to forming more as time goes on. However, each new lump needs to be checked out by your veterinarian (and the "known" lumps rechecked at least annually), as there are other, more serious tumors that can feel like a Lipoma, such as a cutaneous mast cell tumor.
Are Lipomas Ever Malignant?
Yes, although rare, there is a fatty tumor called a liposarcoma, and that is malignant. Metastasis is rare, but due to their nature (infiltrative) they are difficult to fully remove, and recurrence is common.