Low-grade endometrial stromal sarcoma with intracardiac extension - Evolution of extensive smooth muscle differentiation and usefulness of immunohistochemistry for its recognition and distinction from intravenous leiomyomatosis

This case, a rare example of low-grade endometrial stroma sarcoma with exte nsive smooth muscle differentiation which extended to the inferior vena cav a and cardiac chambers closely resembling intravenous leiomyomatosis grossl y and microscopically, illustrates the importance of extensive sectioning a nd the usefulness of immunohistochemistry. Although spindle cell components arranged in interlacing bundles consistent with smooth muscle differentiat ion were recognizable in the primary tumor (on retrospective review), exten sive smooth muscle differentiation in the recurrent tumors masked prototypi cal morphologic features of stromal sarcoma and only small neoplastic strom al components were preserved in limited areas, leading to initial failure t o distinguish the lesion from intravenous leiomyomatosis. The immunophenoty ping disclosed two distinct cell populations in the tumor: i.e. vimentin-po sitive and smooth muscle marker negative stromal cells, and vimentin-negati ve spindle-shaped desmin-positive smooth muscle cells. Our observation sugg ests that the predominance of a smooth muscle component in such a tumor can be misleading and does not always warrant a diagnosis of intravenous leiom yomatosis, nor does it predict a benign clinical course. This case also pro vides an insight into the relationship of the endometrial stroma and myomet rium, and their cell of origin and the histogenesis of endometrial stromal sarcoma.