[Myofibroblastoma of the breast. Report of 8 cases].

Eight cases of breast myofibroblastomas are reported: two in men and six in post-menopausal women. This study and a review of the 19 published cases permit to define more precisely the particular features of this rare and benign mesenchymal tumour. Good demarcation, lack of necrosis and nuclear atypia argue for the benign nature of the lesion. It is made up of spindle cells (mainles myofibroblasts) which are positive for vimentin and not for S 100 protein or epithelial markers. Alpha-smooth muscle cell actin and desmin labelling are heterogeneous. This immunohistochemical study underlines the variable results of myofibroblasts for smooth muscle markers reflecting different degrees in their differentiation, without resolving the question of their origin. A simple surgical excision is required for this benign lesion. No recurrence has never been observed.