Leiomyosarcoma of the os calcis.

A primary leiomyosarcoma of the os calcis, occurring in a 68-year-old woman and treated by below-the-knee amputation, is reported. The diagnosis was confirmed by electron microscopy, and supported by immunochemistry. These techniques can be performed in a primary spindle cell osseous neoplasm to distinguish leiomyosarcoma from fibrosarcoma and malignant fibrous histiocytoma. A total of 28 cases of primary leiomyosarcoma of extragnathic bones have been reported in the literature with one occurring in the foot. This is the first reported case involving the os calcis and the first reported leiomyosarcoma of the foot in the English literature.