Actin-rich (myoepithelial) cells in lobular carcinoma in situ of the breast.

The presence and behaviour of the actin-rich (myoepithelial) cells has been investigated in thirteen cases of lobular carcinoma in situ (L.C.I.S.) of the breast, by means of an immuno-cytochemical method. The technique involved the use of fixed and embedded paraffin sections and of specific antibodies anti-SDS-denatured chicken gizzard actin. The distribution of the myoepithelial cells in L.C.I.S. was not constant. Three main patterns were detected. In some of the lesions the myoepithelial cells were confined to the periphery (pattern A), in others these cells were rather disarranged (pattern B), with neoplastic cells occasionally approaching to the basement membrane. In still other lesions (pattern C), myo-epithelial cells were not present at the periphery, while thin strands of reaction product (probably related to cytoplasmic extensions) were present between the neoplastic cells. Pattern C was present in cases associated with invasive carcinoma. It is suggested that the different patterns of distribution of the myoepithelial cells in L.C.I.S. are progressive, and that they may be of diagnostic importance.