Fine needle aspiration cytology, immunocytochemistry and electron microscopy of fibromatosis of the breast. Report of two cases.

Two cases of primary fibromatosis of the breast are described. The lesions were suspected to be carcinomas both clinically and mammographically. Fine needle aspiration (FNA) yielded bland-appearing isolated spindle cells associated with small groups of benign ductal cells and lymphocytes. Immunoperoxidase staining performed on the original FNA smears showed positivity for vimentin and muscle-specific actin only in the spindle cells and for cytokeratin only in the epithelial cells. Electron microscopy study of one case demonstrated the ultrastructural characteristics of well-differentiated fibroblasts and myofibroblasts.