Uterine composite tumor composed of leiomyosarcoma and embryonal rhabdomyosarcoma with immature cartilage.

We report a rare composite uterine mesenchymal neoplasm in a 66-year-old woman composed of approximately equal amounts of leiomyosarcoma and embryonal rhabdomyosarcoma, the latter containing foci of immature cartilage. Immunohistochemically, both components were positive with desmin. The leiomyosarcomatous element was positive with alpha smooth muscle actin and h-caldesmon and the rhabdomyosarcomatous component with myogenin and myo-D1. In a review of the literature, we have identified only a single example of a similar case. This is likely to represent rhabdomyosarcomatous differentiation in a leiomyomatous neoplasm or alternatively bidirectional differentiation from an uncommitted mesenchymal stem cell.