Myofibroblastoma of the breast is an uncommon benign stromal
tumor encountered predominantly among elderly men. Histologically,
myofibroblastoma is a well-circumscribed
tumor comprised of bipolar spindle cells arranged in short fascicles traversed by
collagen bundles. Based on previous histological, immunohistochemical, and ultrastructural observations, this
tumor is thought to be derived from myofibroblasts. The pathogenesis of
myofibroblastoma is unknown. Given the demographics of this lesion, the established trophic effect of
steroid hormones, and the potential diagnostic utility of
hormone receptor analysis in differentiating spindle cell
tumors, we immunohistochemically tested for
estrogen and
androgen receptors in a host of spindle cell lesions including
myofibroblastoma of the breast. Five cases reported herein of histological confirmed
myofibroblastoma obtained from male and female breasts each showed strong nuclear antibody staining for the
androgen receptor, not seen in four cases of
leiomyosarcoma, three cases of
fibromatosis, three cases of
dermatofibrosarcoma protuberans, and two cases of monophasic
synovial sarcoma. We postulate that the
androgen receptor or its
ligands may be pathologically related to the development of
myofibroblastoma of the breast and diagnostically useful in differentiating it from other spindle cell lesions.