Examination of the TCGA breast cancer dataset revealed higher levels of ID2 and ALDH3A1 expression in triple-negative (ER–/PR–/HER2–) breast cancers compared with HER2+ and ER+/HER2– breast cancers (Fig. 4a), and in ER– versus ER+ breast cancers (Fig. 4b). This evidence concerns the gene PGR and breast cancer.