MYOFIBROSARCOMA OF THE BREAST - REVIEW OF THE LITERATURE ON MYOFIBROBLASTIC TUMORS AND CRITERIA FOR DEFINING MYOFIBROBLASTIC DIFFERENTIATION

A case of myofibrosarcoma of the breast is described. A 55-year-old wo man presented with a small mammary nodule, A large recurrent lesion ap peared a month later, and the patient died 11 months following initial presentation from diffuse pleuropulmonary metastases. Histologically, the primary tumor consisted mainly of spindled cells, arranged in fas cicles and surrounded by varying quantities of dense hyaline collagen. The recurrent lesion had a more pleomorphic organization. In both les ions, there was positive immunostaining for vimentin, smooth-muscle ac tin, and fibronectin, and negative results for desmin, laminin, and ty pe IV collagen. Electron microscopy revealed abundant rough endoplasmi c reticulum, myofilaments with focal densities, and the fibronexus jun ctions and fibronectin fibrils characteristic of myofibroblasts. Given these cellular features and behavior, the tumor was interpreted as a malignant neoplasm showing myofibroblastic differentiation, i,e., a my ofibrosarcoma. This case enlarges the group of myofibrosarcoma of brea st, also with the demonstration of fibronexus and fibronectin fibrils. The paper emphasizes the criteria required for myofibroblastic differ entiation and reviews lesions of the breast reported in the literature as myofibroblastic.