Mammary ducts with and without focal myoepithelial cell layer disruptions show a different frequency of white blood cell infiltration and growth pattern: implications for tumor progression and invasion.

The authors' previous studies revealed that a subset of ductal carcinoma in situ (DCIS) contained focally disrupted myoepithelial (ME) cell layers and basement membrane (BM). As the disruption of these two structures is a prerequisite for tumor invasion, and white blood cells (WBCs) contain digestive enzymes capable of degrading both the BM and damaged host cells, this study was designed to assess the possible roles of WBC in ME cell layer disruptions and tumor invasion. A total of 23 DCIS containing ducts with focally disrupted ME cell layers were selected from 94 such cases identified in the authors' previous studies. Two consecutive sections from each case were double immunostained, one with leukocyte common antigen (LCA) plus smooth muscle actin (SMA) and the other with Ki-67 plus SMA. Ducts lined by at least 50 epithelial cells and distinct ME cell layers were examined. A total of 191 duct cross-sections were found to contain focal ME cell layer disruptions; of these, 186 (97.4%) were with and 5 (2.6%) were without WBC infiltration. Of 207 morphologically similar sections without ME disruptions, 46 (22.2%) were with and 161 (77.8%) were without WBC infiltration. Ki-67-positive cells in ducts with focally disrupted ME cell layers were generally subjacent to ME cell layers, and more than 30 clusters of multiple proliferating cells were seen directly overlying or near focally disrupted ME cell layers. In contrast, Ki-67-positive cells in ducts without ME disruptions were scattered over the entire epithelial compartment. The significantly different frequency of WBC infiltration and clusters of multiple proliferating cells in ducts with and without ME disruptions suggests that WBCs might play important roles in ME disruption and tumor invasion.