Myofibroblasts in human breast tumors: an ultrastructural study.

Myofibroblasts were observed in the stroma of breast tumors in all cases examined by electron microscopy; 1 intraductal papillomatosis, 1 papillary carcinoma and 7 infiltrating duct carcinomas. The tubule- or duct-like structure in the tumor tissue were frequently surrounded by myofibroblasts which corresponded to delimiting fibroblasts in the normal breast tissue. In infiltrating duct carcinomas without tubule-like structures, myofibroblasts occurred dispersely in the stroma and they might correspond to fibroblasts in normal connective tissue. A possible role of these myofibroblasts as mesenchymal cells activated in a tumorous condition was discussed.