Smooth muscle tumours of the external genitalia: clinicopathological analysis of a series.

Smooth muscle tumours of the external genitalia (vulva, scrotum and nipple) are uncommon and have received little attention in the literature. Given their purported close relationship to cutaneous (pilar) leiomyomatous lesions, we have studied 32 cases (18 vulva, 10 scrotum, four nipple) from 31 patients in order to compare clinicopathological features at the different sites. Only those in the nipple were comparable in size and histology to pilar leiomyomas. Vulval and scrotal tumours tended to be much larger and better circumscribed. Purely epithelioid lesions were only identified in the vulva (two cases) and at this site myxoid change and hyalinization were substantially more common. Almost all cases showed immunohistochemical evidence of muscle differentiation. On histological grounds, nine cases were classified as leiomyosarcoma (six scrotum, three vulva) but only one of the five with follow-up has led to the patient's death. With the exception of nipple lesions, which are particularly uncommon, we would not support the traditional inclusion of genital smooth muscle tumours under the general heading of cutaneous leiomyoma/sarcoma, as vulval and scrotal lesions are clinicopathologically quite different.