Pleomorphic rhabdomyosarcoma in adults: A clinicopathologic study of 38 cases with emphasis on morphologic variants and recent skeletal muscle-specific markers

Pleomorphic rhabdomyosarcoma (PRMS) is a rare and controversial tumor of sk eletal muscle phenotype. Diagnostic criteria for PRMS by combined histology and currently available immunohistochemistry have not been clearly defined . We report 38 pleomorphic rhabdomyosarcomas in adults, explore morphologic variants, and discuss our experience with both specific and nonspecific sk eletal muscle markers in these tumors. Clinical data, morphology, and immun ohistochemistry were reviewed. Electron microscopy was performed. Of 38 cas es, there were 28 males and 10 females. Patient ages ranged from 21 to 81 y ears (median = 54 y; mean = 51 y). Tumors were located in the lower extremi ty (n = 18), abdomen/retroperitoneum (n = 6), chest/abdominal wall (n = 5), spermatic cord/testes (n = 4), upper extremity (n = 3), and one each in th e mouth and orbit. Tumor sizes ranged from 1.5 to 15.0 cm (mean = 7.3 cm; m edian = 6.8 cm). The cases were divided into three variants, each with larg e, atypical, pleomorphic polygonal rhabdomyoblasts (PRMB) with abundant eos inophilic cytoplasm in varying numbers and different morphologic background s of round or spindled rhabdomyoblasts (RMB).1. Classic PRMS: Predominantly atypical PRMB in sheets (n = 8).2. Round cell PRMS: Clusters of PRMB throu ghout the tumor with a background of slightly atypical, medium-sized, round , blue RMB (n = 13).3. Spindle cell PRMS: Scattered PRMB in a predominance of atypical spindled RMB arranged in a storiform growth pattern (n = 17). I mmunohistochemistry revealed the following: myoglobin (37/38), MyoD1 (19/36 ), skeletal muscle myogenin (myf4; 19/34), fast skeletal muscle myosin (4/5 ), desmin (36/38), muscle-specific actin (MSA; 25/35), smooth muscle actin (SMA; 15/33), and muscle specific myogenin (myf3; 25/35). Immunohistochemis try was supportive of skeletal muscle differentiation with at least one pos itive skeletal muscle-specific marker (myoglobin, MyoD1, fast skeletal musc le myosin, or myf4). In addition, all cases had some positivity for nonspec ific muscle markers (desmin, MSA, SMA, myf3). Electron microscopy (EM), per formed on eight selected cases from all three morphologic groups, demonstra ted definitive skeletal muscle differentiation in all cases. Follow-up, ava ilable on 30 (79%) cases, revealed that 70% of patients died of disease (me an 20 months, range 1 month-108 months), 3% were alive with disease at 12 m onths (n = 1); and 27% had no evidence of disease (mean, 83 mo; range, 18 t o 108 mo). PRMS, a tumor of predominantly middle-aged adult males in the lo wer extremity, can be diagnosed by the morphologic presence of scattered PR MB with immunohistochemical evidence of at least one skeletal muscle-specif ic marker. There are three morphologic variants of PRMS. The appropriate di agnosis of PRMS is significant as it is a high-grade sarcoma, with an aggre ssive clinical course.