The last finding, together with the facts that (a) in this study 95% of PR+ and 43% of PR- breast cancer were also ER+ breast cancer; (b) a significant association defined for ER+, but not for ER- breast cancer with potential heterogeneity (P = 0.07) in overall group and significant heterogeneity (P = 0.04) in postmenopausal women, leads us to believe that ER status may explain the significant association of alcohol with PR+ breast cancer and, in part, with PR- breast cancer. This evidence concerns the gene ESR1 and breast cancer.