A lipoma is a benign tumor composed of adipose tissue (body fat). It is the most common benign form of soft tissue tumor. Approximately one percent of the general population has a lipoma. These tumors can occur at any age, but are most common in middle age, often appearing in people from 40 to 60 years old.
Genetic studies in mice have shown a correlation between the HMG I-C gene (previously identified as a gene related to obesity) and lipoma development.