OBJECTIVETo investigate the clinicopathologic characteristics, differential diagnosis and biologic behaviors of pleomorphic rhabdomyosarcoma (PRMS).

METHODSThe clinical findings, pathological features and immunophenotypes were reviewed in 44 cases of PRMS (encountered during the period from 2005 to 2012). The clinical outcome was analyzed.

RESULTSThere were 33 males and 11 females with age ranging from 2 to 85 years (mean, 51 years; median, 55 years). Of 44 tumors, 22 occurred in the extremities (50.0%), 16 in the trunk (36.4%), 5 in the internal organs (11.4%), and 1 in the head and neck (2.2%). Histologically, 40 tumors showed features of pleomorphic sarcoma with striking resemblance to undifferentiated pleomorphic sarcoma (UPS)/malignant fibrous histiocytoma(MFH). However, variable amount of pleomorphic rhabdomyoblasts (PRMB) were identified in most cases. The remaining 4 tumors were composed predominantly of fascicles of spindle cells with interspersed PRMBs. Immunohistiochemically, tumor cells showed diffuse staining of desmin (41/41,100%), with variable expression of myogenin (18/32, 56.3%), MyoD1 (10/21, 47.6%) and MSA (21/29, 72.4%), whereas α-SMA was negative in most cases. Follow-up data (range, 2 to 51 months) available in 29 cases showed 12 patients were alive with unresectable or recurrent disease and 17 patients were alive with no evidence of disease. The median disease-free and overall survivals was 6.0 months (mean, 9.1 months) and 8.0 months (mean, 11.2 months) respectively. Thirteen patients (44.8%) exhibited progression of disease with recurrence in 4 cases and metastasis in 9 cases. The median interval to progression was 6.0 months (mean, 5.9 months).

CONCLUSIONSThe presence of pleomorphic cells with strong eosinphilic cytoplasm in a pleomorphic sarcoma is suggestive of a PRMS. Diffuse, strong expression of desmin and negative staining for α-SMA further facilitate the diagnosis of PRMS and its differential diagnosis from pleomorphic leiomyosarcoma. Although PRMS may affect children or adolescents, it should be cautious not to misdiagnose anaplastic rhabdomyosarcoma as PRMS. PRMS is a high-grade sarcoma with a poor prognosis.