A benign lipoma is a collection of fatty cells that form a lump, or a fatty tumor, underneath the skin. They are usually located between the skin and the muscular layer beneath the skin. Benign lipomas are not cancerous and are usually harmless. They are the most common type of soft tissue tumor. Benign lipomas are most often found on the shoulders, arms, trunk and back. However, they can occur anywhere in the body. Benign lipomas are very rare - about one percent of the population has at least one lipoma.