Epithelioid component of uterine leiomyosarcoma simulating metastatic carcinoma

A variant of uterine leiomyosarcoma containing two morphologic bell populations is described. A smooth-muscle component with a mitotic rate of 13 per 10 high-power fields, and a second population of cells mimicking metastatic small-cell carcinoma were both present. The second population was composed of small angulated epithelioid cells with hyperchromatic nuclei and barely discernible cytoplasm growing in tight rows, often in single file between fascicles of smooth muscle. DNA flow cytometry showed a large tetraploid aneuploid tumor cell population, and further suggested that the epithelioid cells probably represent tetraploid tumor cells in S-phase. Thus, this morphologic variant of leiomyosarcoma, unlike previously described variants of smooth-muscle tumors, is explained by the variable appearance of the neoplastic cells in different phases of the cell cycle.