Well-differentiated liposarcoma (atypical lipomatous tumors).

Well-differentiated (WD) liposarcoma accounts for about 40% to 45% of all liposarcomas therefore representing the larger subgroup of adipocytic malignancies. It tends to occur equally in the retroperitoneum or the limbs followed by the paratesticular area and the mediastinum, with a peak incidence between the fifth and the seventh decades. WD liposarcoma is further subdivided in the adipocytic (lipoma-like), sclerosing, inflammatory, and spindle cell subtypes, of which the first two are by far the commoner. WD adipocytic liposarcoma is composed of a relatively mature adipocytic proliferation, featuring cell size variation as well as at least focal nuclear atypia. A varying number (from many to none) of lipoblasts may be found. Sclerosing WD liposarcoma is characterized microscopically by the presence of scattered distinctive bizarre stromal cells and multivacuolated lipoblasts set in a fibrillary collagenous background. Inflammatory liposarcoma represents a rare variant of WD liposarcoma in which a chronic inflammatory infiltrate predominates to the extent that the differential diagnosis is mainly with nonadipocytic lesions such as inflammatory myofibroblastic tumor, Castleman's disease, and Hodgkin's as well as non-Hodgkin's lymphomas. Spindle cell liposarcoma is the rarest variant and is composed neural-like spindle cell proliferation set in a fibrous and/or myxoid background and associated with an atypical lipomatous component which usually includes lipoblasts. Cytogenetically, WD liposarcoma appears to be relatively homogenous exhibiting characteristic ring as well as giant marker chromosomes containing amplified genetic material derived from the 12q13-15 chromosome region. As WD liposarcomas of any type have no potential for metastasis unless they undergo dedifferentiation, the opportunity to replace the term "WD liposarcoma" with a less frightening denomination has produced a long, sharp debate. WD liposarcoma and atypical lipoma should be considered as synonyms and their use should therefore be determined by the degree of reciprocal comprehension between the surgeon and the pathologist to prevent either inadequate or excessive treatment.