In addition, it has been reported that SOX9 maintains the luminal stem/progenitor lineage, to which POU2F3-expressing cells often belonged in our analysis, in normal mammary glands, and SOX9 upregulation could drive luminal-to-basal reprogramming and induce, generally triple-negative, basal-like breast cancers [21, 33]. Here, SOX9 is linked to breast cancer.