Myoepithelial cells in lobular carcinoma in situ of the breast: a parallel immunocytochemical and ultrastructural study.

The distribution and morphology of myoepithelial cells in one case of normal breast and in 4 cases of lobular carcinoma in situ (LCIS) were studed by immunoperoxidase and immunofluorescence with anti-actin antisera and by electron microscopy. The actin-rich cells appeared to lay flattened on the basement membrane, or perpendicular to it, or appeared dislodged toward the center of the neoplastic ductules in the different cases. It is proposed that the presence of actin-rich cells inside the neoplastic aggregates represents a process of colonization of lobular carcinoma by myoepithelial cells dislodged from the basement membrane; a differentiation of some neoplastic cells toward myoepithelial elements might also be taken into consideration. The features here described could identify a preinvasive stage of LCIS.