Lipomas are common, benign tumors composed of mature fat cells enclosed in a thin capsule. They sit most often in the subcutaneous (just under the skin) layer, feel soft and mobile, and grow slowly over months to years. Variants include angiolipomas (can be tender due to small blood vessels) and less common types that contain fibrous tissue. Deeper lipomas can occur within muscle (intramuscular) or along fascial planes.
Lipomas are not cancers and do not “turn into” liposarcoma. However, certain features (deep location, rapid growth, firmness, size >5 cm) can mimic atypical lipomatous tumors/liposarcoma—those require closer evaluation and pathology to be sure.