RESUMEN
Myofibroblastoma of the breast is a recently described entity. Since its first description in 1987, less than 50 cases have been reported. We present the first (reported) myofibroblastoma to be detected as a non-palpable mass on a routine screening mammogram and emphasize the importance of not mis-diagnosing this rare cellular lesion as malignant on frozen section. Review of the literature demonstrates changes in the clinical presentation of myofibroblastomas. Once considered more common in men than in women, myofibroblastomas are now being reported with increasing frequency in women. The age at presentation is a decade earlier, and not surprizingly, the size of the earlier detected lesion is smaller. Recently four different cytoskeletal phenotypes (V, VA, VAD and VD) of myofibroblastomas have been described, depending upon the vimentin (V), actin (A), and desmin (D) immunoreactivity. Whereas vimentin reactivity is universal, actin and desmin immunoreactivity is variable, desmin being more frequently positive than actin. As more is known about the clinical behavior of myofibroblastomas, their rate of recurrence and malignant potential, if any, the relationship of the cytoskeletal content to prognosis may become clearer. Currently, complete immunohistochemical analysis and electron microscopic examination of this interesting breast lesion is recommended. List of abbreviations-Vimentin (V), actin (A), and desmin (D), vimentin and actin (VA), vimentin and desmin (VD), vimentin, actin and desmin (VAD).