GIANT MYOFIBROBLASTOMA OF THE MALE BREAST

Myofibroblastoma of the breast is a rare, benign neoplasm, seen predom inantly in men. The gross appearance is that of a well-circumscribed n odule, characteristically small, seldom exceeding 3 cm. We report a ca se of giant myofibroblastoma measuring 10 cm and weighing 169 g in the breast of an 83-year-old man. Light microscopic, immunohistochemistry , and electron microscopic features are described. Histologically, the se neoplasms may exhibit a varied cellularity that can be misinterpret ed as sarcoma. However, they lack marked cellular pleomorphism, tumor necrosis, and mitosis and are characteristically composed of plump and long bipolar, spindly cells arranged in swirling fascicles with inter vening broad collagen bands. As we report, immunostaining is strongly positive for vimentin, desmin, and muscle common antigen and negative for cytokeratins and S-100-associated protein. Electron microscopy sho ws predominantly cells suggestive of myofibroblastic differentiation. The patient has remained free of disease 2 years after mastectomy.