Smooth Muscle and Nerve Sheath Tumors of the Breast

The clinical and pathological features of 22 smooth muscle tumors and 23 nerve sheath tumors of the breast are presented. The smooth muscle tumors included 18 leiomyomas and 4 leiomyosarcomas. Two types were found: those superficial in the nipple or in the skin overlying the breast and those located within the breast parenchyma. Superficial leiomyomas were small and had ill-defined, infiltrating margins. Leiomyomas located within the breast were circumscribed and larger than the superficial ones. Mitotic activity did not exceed 1 mitotic figure per 10 high-power field and only 2 of the 18 showed 1 + and 2 + atypia. None recurred after local excision. The four leiomyosarco mas had 2 + and 3 + nuclear atypia and mitotic activity ranging from 3 to 28 mitotic figures per 10 high-power field. Recurrences occurred in two, but none metastasized. Nerve sheath tumors included 5 neurilemomas, 15 neurofibromas and 3 malignant schwannomas. All neurilemomas were encapsulated and showed no mitotic activity or cytologic atypia. Of the 15 neurofibromas, 6 were encapsulated, 4 had circumscribed margins with focal infiltration, and 2 had infiltrative margins. Focal cytologic atypia was seen in 4. All 3 malignant shwannomas had infiltrative margins, nuclear atypia, and noticeable, often abnormal, mitotic figures. Two of the 11 patients with neurofi broma had von Recklinghausen's disease and developed recurrences. None of the 3 patients with malignant schwannoma developed a recurrence. Int J Surg Pathol 2(2): 85-92, 1994