Leiomyoma of the mandible: a rapid growing case with immunohistochemical and electron microscopic observations.

A rare case of leiomyoma of the mandible is reported together with the conventional histologic, immunohistochemical, and electron microscopic findings. On immunohistochemical evaluation the tumor cells were positive for vimentin, desmin, and alpha-smooth muscle actin but negative for neurogenic antigens and markers for vascular endothelial cells. Ultrastructural examination revealed smooth muscle cell differentiation. The Ki-67 labeling index was 4.7%. The tumor showed rapid increase in size and clinical features suggestive of malignancy. However, on histopathologic evaluation it was diagnosed as a benign neoplasm, and this diagnosis was supported by the results for mitotic rate, Ki-67 labeling index, and p53 immunostaining.