Composite uterine neoplasm with embryonal rhabdomyosarcoma and primitive neuroectodermal tumor components: rhabdomyosarcoma with divergent differentiation, variant of primitive neuroectodermal tumor, or unique entity?

Three cases of composite uterine neoplasms comprised of primitive neuroectodermal tumor (PNET) and rhabdomyosarcoma (RMS) have previously been described, including only one wherein the rhabdomyosarcomatous component was of the embryonal subtype. Whether such composite neoplasms are a variant of RMS, a variant of PNET, or a unique entity is unknown. We report the clinicopathologic, immunohistochemical, and molecular cytogenetic findings in a case of uterine embryonal RMS with coexisting PNET that was diagnosed in a 25-year-old female. The tumor broadly involved the cervix and corpus uteri and resulted in uterine inversion. The 2 distinct components each showed classic morphologic features, including cartilage in the RMS component. The unique combination of histologic, immunohistochemical and molecular findings in composite neoplasms of this type raises a question of whether they should be classified and treated as RMS, PNET, or a unique high-grade sarcoma. A variety of clinicopathologic arguments are presented that support the notion that the current neoplasm is an embryonal rhabdomyosarcoma with divergent neuroectodermal and cartilaginous differentiation.