PLEOMORPHIC SOFT-TISSUE MYOGENIC SARCOMAS OF ADULTHOOD - A REAPPRAISAL IN THE MID-1990S

Among 325 diverse sarcomas, 39 rhabdomyosarcomas (RMS), including all histologic variants, and 135 leiomyosarcomas (LMS) were identified. Wi thin these two groups, 18 (46%) of the RMS and 14 (10%) of the LMS rep resented pleomorphic variants. These neoplasms were studied by morphol ogy (histology and ultrastructure) and by immunohistochemical methods employing antibodies to intermediate filaments (vimentin and desmin) a nd actin isoforms [alpha-smooth (sm) and alpha-sarcomeric (sr) actins] . Twenty-four pleomorphic malignant fibrous histiocytomas (MFH) and ei ght pleomorphic liposarcomas (LS) were examined in a similar fashion. By light microscopy, the pleomorphic RMS, LMS, and MFH were indistingu ishable, as each was dominated by pleomorphic cells disposed in a haph azard growth pattern; moreover, many featured fascicular, storiform, a nd sclerotic zones. The distinction between these neoplasms became app arent only following immunohistochemistry and/or ultrastructural study . All pleomorphic RMS disclosed rudimentary sarcomeres and exhibited t he following cytoskeletal profile: vimentin(+) (18 of 18), desmin (+) (14 of 18), a-sr actin(+) (18 of 18) and alpha-sm actin(+) (five of 18 ). All the pleomorphic LMS featured smooth-muscle differentiation of v ariable degrees in the form of cytoplasmic bundles of microfilaments a nd associated dense bodies; their cytoskeletal profile was vimentin () (14 of 14), desmin (+) (seven of 14), alpha-sr actin (+) (none of 14 ), and alpha-sm actin(+) (eight of 14). The latter was demonstrated in all moderately differentiated, but absent or only focally expressed i n poorly differentiated variants. All pleomorphic MFH and LS were devo id of myogenic (skeletal or smooth) ultrastructural features and expre ssed vimentin solely. This combined morphological and immunohistochemi cal study illustrates the following: First, these pleomorphic sarcomas are often indistinguishable by histologic growth pattern alone; thus, an accurate diagnosis requires study with all of these techniques. Se cond, pleomorphic myogenic sarcomas are restricted to adults and are n ot uncommon neoplasms among pleomorphic sarcomas: RMS (28%), LMS (21%) , MFH (38%), and LS (13%). Third, the study defines desmin-negative an d alpha-sm actin-positive pleomorphic RMS, and desmin-negative and alp ha-sm-actin-negative pleomorphic LMS.