In this article, we supplement the few published articles by describing the clinical and pathologic features of pleomorphic and dedifferentiated leiomyosarcoma from 41 patients (27 women and 14 men) with an age range of 25 to 75 years (mean, 56.5 years), representing the largest cohort reported to date. The typical leiomyosarcoma component accounted for <5% to 60% (mean, 15%) of the tumor. The pleomorphic sarcoma component was composed of polygonal cells in 57% of cases, spindle cells in 21%, a combination of polygonal, epithelioid, rhabdoid, and/or spindle cells in 18%, and predominantly epithelioid cells in 3%. The classical leiomyosarcoma component was positive for at least one myogenic immunohistochemical marker in 29 tumors tested; smooth muscle actin in 100% (27/27), calponin in 90% (9/10), muscle-specific actin in 90% (10/11), desmin in 86% (23/27), smooth muscle myosin heavy chain (SMMS-1) in 67% (4/6), and caldesmon in 57% (4/7). The pleomorphic sarcoma component was reactive for at least one muscle marker in 77% (23/30) of cases; smooth muscle actin in 63% (17/27), calponin in 60% (6/10), SMMS-1 in 60% (3/5), desmin in 59% (16/27), muscle-specific actin in 40% (4/10), and caldesmon in 29% (2/7). The classical leiomyosarcoma component was often strongly positive for myogenic markers, and the pleomorphic sarcoma component usually showed focal and less intense immunoreactivity. Based on staining for muscle markers in the pleomorphic component, twenty-three cases were designated as pleomorphic leiomyosarcoma, and 7 cases were designated as dedifferentiated leiomyosarcoma (negative for all muscle markers used). Eleven cases, in which tissue was not available for immunhistochemical stains, the question of pleomorphic versus dedifferentiated leiomyosarcoma could not be answered. The incidence of metastasis was 89% (32/36) and the mortality rate was 50% (18/36) at last follow-up (3-104 months; mean, 27.5 months).
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