Cao L, et al. - The association between prostate-derived ETS factor (PDEF) and androgen receptor (AR) in ER^– breast cancer (BC) was examined in this analysis. This relationship was immunohistochemically assessed in 246 cases of ER^– invasive BC, as was their relationship in ER^– BC cell lines. Researchers reported that PDEF was correlated with markers of bad prognosis and strongly associated with AR expression in ER^– breast cancer. These findings support its role as a growth promoter in ER^– BC, and reveal it could be a downstream target gene of AR and an independent predictor of OS.