The 3-layered ductal epithelium in gynecomastia.

Gynecomastia is the most common abnormality in the male breast and has been associated with male breast cancer, but whether there is an etiological role remains unknown. In the present study we conducted an immunohistochemical investigation to further characterize gynecomastia. A total of 46 cases of gynecomastia were immunohistochemically stained on tissue microarrays for estrogen receptor (ER), progesterone receptor, HER2, androgen receptor, cytokeratins (CK5, CK14, CK7, and CK8/18), p63, E-cadherin, BRST2, cyclin D1, Bcl-2, p53, p16, p21, and Ki67. In addition, 8 cases of male ductal carcinoma in situ and normal breast tissue obtained from autopsies (n = 10) and adjacent to male breast cancer (n = 5) were studied. Normal ductal male breast epithelial cells were very often ER and Bcl-2 positive (> 69%), and progesterone receptor and androgen receptor expression was also common (> 39%). Gynecomastia showed a consistent 3-layered pattern: 1 myoepithelial and 2 epithelial cell layers with a distinctive immunohistochemical staining pattern. The intermediate luminal layer, consisting of vertically oriented cuboidal-to-columnar cells, is hormone receptor positive and expresses Bcl-2 and cyclin D1. The inner luminal layer is composed of smaller cells expressing CK5 and often CK14 but is usually negative for hormone receptors and Bcl-2. Male ductal carcinoma in situ was consistently ER positive and CK5/CK14 negative. In conclusion, for the first time we describe the 3-layered ductal epithelium in gynecomastia, which has a distinctive immunohistochemical profile. These results indicate that different cellular compartments exist in gynecomastia, and therefore gynecomastia does not seem to be an obligate precursor lesion of male breast cancer.