PLEOMORPHIC RHABDOMYOSARCOMA IN ADULTHOOD - ANALYSIS OF 11 CASES WITHDEFINITION OF DIAGNOSTIC-CRITERIA

Currently, pleomorphic rhabdomyosarcoma (RMS) in adults is considered to be extremely rare or nonexistent. The authors have identified 11 ca ses of pleomorphic RMS using the following criteria: pleomorphic sarco ma occurring within voluntary muscle, large polygonal or strap-like ce lls with copious eosinophilic cytoplasm, desmin and myoglobin immunore activity, or ultrastructural evidence of sarcomeric differentiation. T en patients were male, the median age at presentation was 56 years (ra nge, 27-84), and the thigh (seven cases) was the most common site. Of eight cases with clinical follow-up, one patient is alive at 20 months , and seven died 2 to 28 months following diagnosis. The tumors were g enerally patternless, but several had storiform areas. Cross-striation s were not identified. Immunostaining for muscle-related antigens was positive as follows: desmin (in 10 of 11 cases), myoglobin (in 10 of 1 1 cases), actin HHF-35 (in all 11 cases), smooth-muscle actin (in six of eight cases), sarcomeric actin (in six of nine cases), and fast myo sin (in five of five cases). Staining for S-100 protein was negative i n all cases. On electron microscopy (six cases), two tumors had well-d ifferentiated rhabdomyoblasts with sarcomeres, Z-disks, and hexagonal arrays of myofilaments; three were poorly differentiated; and one cont ained immature mesenchymal cells only. Pleomorphic RMS can be distingu ished from other pleomorphic sarcomas provided that well-fixed tumor t issue is available for immunohistochemical staining and electron micro scopy. We consider that this distinction is important in view of the p oor prognosis associated with pleomorphic RMS in this series.