Neoplasms showing lipomatous differentiation comprise the numerically largest family of neoplasms in man. They can occur at almost all body sites and display a wide age spectrum ranging from infancy to late adult life. Benign lipomas are most frequent in patients between 40 and 60 years of age while liposarcomas most often come to clinical attention in patients over 50 years of age.
Neoplasms showing true lipomatous differentiation express S-100 protein. Additionally, benign lipomatous neoplasms display a variety of translocations, rearrangements, and other genetic alterations which include translocations involving 12q13–15, 8q11–13, 11q13, and 10q22. Lipomas of usual type show deletions of 13q, while spindle cell and pleomorphic lipomas show loss of 16q13.
Of diagnostic importance is the CHOP gene rearrangement characteristic of myxoid and round cell liposarcomas and amplification of the MDM2 gene in well differentiated liposarcomas and atypical lipomatous neoplasms. This gene amplification helps distinguish these neoplasms from benign lipomas.
Lipomas occur as both solitary and multiple lesions. Most are removed for cosmetic purposes. Lipomas are rare before 20 years of age but gradually increase in frequency with a maximum prevalence in patients 40 to 60 years old. The frequency of lipomas does not vary with race. Men appear to be more frequently affected.
Lipomas may occur as either superficial or deep neoplasms and, in both locations, are usually asymptomatic slowly growing masses. Pain is rarely apparent in ordinary lipomas, but angiolipomas are often painful. Imaging studies are helpful in identifying a lesion as fatty in nature but are of less aid in separating benign from malignant neoplasms. Magnetic resonance imaging studies of both benign and malignant lipomatous neoplasms demonstrate high signal intensity on T1-weighted images.