bcl-2 expression in normal breast tissue during the menstrual cycle.

bcl-2 is a proto-oncogene discovered through the t(14;18) translocation occurring in most human follicular lymphomas. The function so far attributed to bcl-2 is to counteract the occurrence of apoptosis and to prolong cell survival without affecting the cycling cells. Apoptosis has been described in normal breast tissue epithelial cells, and it peaks at the end of the luteal phase. We have studied bcl-2 expression by an immunohistochemical method in 50 samples of normal breast tissue distributed throughout the menstrual cycle. bcl-2 staining predominated in the lobular epithelial cells. It displayed a striking cyclic variation, with maximal expression at the mid-cycle period and a sharp decrease at the end of the cycle. These results strongly suggest that the regulation of bcl-2 expression in breast tissue is hormone-dependent. This could be of significance in tumorigenesis.