A lipoma is a benign tumor that is made up of fatty tissue. They usually manifest as small, soft, painless movable lumps on the skin, but can be up to six centimeters across and can occur throughout the body. They most often appear in adults aged 40-60. They occur in about 1% of the population. It does not appear that they ever become malignant, although research on the issue continues.
On the whole, lipomas are completely harmless and asymptomatic, and don't require treatment. They may have to be removed surgically if they restrict movement or for cosmetic purposes. This is usually an outpatient procedure done under local anesthetic. They may have to be biopsied to rule out more serious types of cancer.