Rhabdomyosarcoma in adults.

Rhabdomyosarcomas occur in adults in one of two forms; as sporadic cases of the juvenile histological types and more commonly, if controversially, as the major adult form, pleomorphic rhabdomyosarcoma. This review documents the historical background to the fluctuating diagnostic popularity of pleomorphic rhabdomyosarcoma, together with a presentation of its defining clinicopathologic characteristics, and presents the clinicopathologic features of the juvenile types as they occur in adults. The concept of pleomorphic rhabdomyosarcoma as a distinct clinicopathologic entity, presenting as an aggressive, predominantly spindle-cell tumor arising in the skeletal musculature of middle-aged adults and defined by the presence of large, pleomorphic tumor cells, which show, at least focally, immunophenotypic or ultrastructural sarcomeric muscle differentiation, is discussed and supported.