Our data show that the expression of POLR3G in breast cancer samples was negatively correlated with that of eight out of ten genes (GATA3; XBP1; AGR2; SIDT1; AR; SPDEF; FOXA1; MLPH; Table S2) in a list of signature genes most differentially expressed in luminal A compared to basal-like tumors [27]. This evidence concerns the gene XBP1 and breast cancer.