Atypical stromal smooth muscle hyperplasia of prostate.

A prostatic lesion was resected but recurred six years later with the same atypical smooth muscle hyperplasia in the stroma and without glandular atypia. Ultrastructural study confirms the smooth muscle origin and its atypicality. Review of previous reports of leiomyosarcoma of the prostate show that the minimum criteria for malignancy are gross evidence of capsular invasion and one to two mitotic figures per ten high-power field. Cellular pleomorphism and cellularity by themselves are insufficient to diagnose sarcoma.