Uterine mixed embryonal rhabdomyosarcoma and fetal rhabdomyoma.

A polypoid uterine tumor, occurring in a 31-year-old woman, with histopathologic features of both embryonal rhabdomyosarcoma and fetal rhabdomyoma is reported. The clinical and pathologic differences between pure fetal rhabdomyoma and embryonal rhabdomyosarcoma are detailed and theories concerning the histogenesis of such a mixed, or intermediate, tumor are discussed. Most likely, this neoplasm represents one example in a spectrum of tumors with varying proportions of immature and mature skeletal muscle elements. Its good prognosis is in keeping with that of uterine (cervical) embryonal rhabdomyosarcomas in general, although the presence of mature skeletal muscle elements may signify an even better prognostic group of tumors.