Lipomas are benign tumors that originate from fat cells. “Lip” in Latin stands for fat and “oma” stands for tumor. They are the most common tumor seen in dogs and are most common in overweight, middle-age to older dogs. The exact cause of the formation of these tumors is unknown. They are common in all breeds, but especially in Labrador retrievers.
Lipomas are well-defined, oval or round growths that exist and can be easily felt under the skin, or the subcutaneous area of the body. They usually feel soft and smooth, and can be easily moved around under the skin. Most occur on the trunk of the dog, especially under the chest. They can also occur on the legs and neck. They start off small, but can grow as large as an orange. Most lipomas do not cause any clinical signs. They are removed surgically for cosmetic reasons or if they occur in the joints of the dog and are causing gait abnormalities. In rare instances, lipomas can develop in the abdomen, chest or behind the eye. These lipomas can cause serious problems and must be removed surgically.
Lipomas can mimic other, more malignant tumors. Your vet will almost always want to stick a needle into the lipoma, aspirate a sample of cells and confirm that only fat cells are noted under the microscope. Biopsy of the tumor (taking a small sample of the tumor surgically) will also show that the tumor is benign.
Most lipomas only require monitoring of their size, growth and any change in their appearance. If any marked change in their appearance occurs, your veterinarian should repeat a cytology exam. Some lipomas penetrate or infiltrate deeply into surrounding muscle tissue. Those are called infiltrative lipomas. They can cause lameness due to the impairment of proper muscle function. Infiltrative lipomas can be difficult to remove surgically and can recur post-operatively. Recurrence is rare post-operatively for noninvasive lipomas.
Monitoring the size and growth rate of any mass on a dog is important and should be done on a monthly basis at home and annually by your veterinarian. Report any change in tumor size, shape or firmness to your veterinarian.