ObjectiveTo investigate the pathological characteristics, diagnosis, and differential diagnosis of embryonal rhabdomyosarcoma (ERMS) in the male reproductive system.

METHODSWe obtained the clinicopathological features, immunophenotypes, and electron microscopic findings of 11 male patients with ERMS in the reproductive system from 2000 to 2015, analyzed the data, and reviewed relevant literature.

RESULTSERMS developed in these patients at a median age of 17 (9－58) years, 3 cases in the testis, 4 in the scrotum, 1 in the epididymis, and 3 in the prostate. ERMS presented no clinical specificity, which made it difficult to be differentiated from inflammatory and other benign lesions. Microscopically, the tumor cells were arranged in a diffuse or fascicular distribution and mainly composed of short spindle-like, round, or irregularly shaped cells with nuclear hyperchromatism, the cytoplasm strongly eosinophilic, with differentiation of the striated muscle. Some of the cells were naively differentiated or tennis racket-shaped and some exhibited vacuolar degeneration in the cytoplasm. The nuclei were round or short spindle-shaped with visible nucleoli and mitoses. Immunohistochemically, the tumor cells were positive for Myogenin (5/6), Desmin (11/11), MyoD1 (8/9), and Myosin (1/2). Electron microscopy revealed early myofibrils in the cytoplasm of the tumor cells.

CONCLUSIONSERMS is a rare and highly malignant tumor characterized by local invasion and early metastasis and apt to develop in the reproductive system of young males. The diagnosis of the malignancy is mainly based on its histopathological and immunohistochemical manifestations, combined with electron microscopy when necessary. Early surgical resection in combination with radio- and chemotherapy is recommended for its treatment, which could reduce the recurrence of the tumor and improve the survival of the patients.