Well-differentiated liposarcoma (atypical lipomatous tumors)

Well-differentiated (WD) liposarcoma accounts for about 40% to 45% of all l iposarcomas therefore representing the larger subgroup of adipocytic malign ancies. It tends to occur equally in the retroperitoneum or the limbs follo wed by the paratesticular area and the mediastinum, with a peak incidence b etween the fifth and the seventh decades. WD liposarcoma is further subdivi ded in the adipocytic (lipoma-like), sclerosing, inflammatory, and spindle cell subtypes, of which the first two are by far the commoner. WD adipocyti c liposarcoma is composed of a relatively mature adipocytic proliferation, featuring cell size variation as well as at least focal nuclear atypia. A v arying 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 f ibrillary collagenous background. Inflammatory liposarcoma represents a rar e variant of WD liposarcoma in which a chronic inflammatory infiltrate pred ominates to the extent that the differential diagnosis is mainly with nonad ipocytic lesions such as inflammatory myofibroblastic tumor, Castleman's di sease, and Hodgkin's as well as non-Hodgkin's lymphomas. Spindle cell lipos arcoma is the rarest variant and is composed neural-like spindle cell proli feration set in a fibrous and/or myxoid background and associated with an a typical lipomatous component which usually includes lipoblasts. Cytogenetic ally, WD liposarcoma appears to be relatively homogenous exhibiting charact eristic ring as well as giant marker chromosomes containing amplified genet ic material derived from the 12q13-15 chromosome region. As WD liposarcomas of any type have no potential for metastasis unless they undergo dediffere ntiation, 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 t herefore be determined by the degree of reciprocal comprehension between th e surgeon and the pathologist to prevent either inadequate or excessive tre atment. Copyright (C) 2001 by W.B. Saunders Company.