KRT18 and breast cancer: Thus, we divided HR+ BC-PDMs into four groups based on the evaluated CK expression: CK5−/CK18+ (luminal, differential glandular phenotype), CK5+ (basal), CK5/6+ (basal, stem cell phenotype) and CK5/6/18+ (intermediate glandular phenotype) [48] (Fig. 3C).