There was the expected close correlation between the ESR1 transcript levels and commonly observed ESR1 coexpressed genes (for example, GATA3) as well as other genes (for example, KRT8, KRT18) that characteristically define luminal-type breast cancer, although this tumor collection also contained several ERBB2-positive cases (10/101) that are not characteristically found in microarray-defined clusters of luminal-type breast cancer [38,39,49-51]. Here, ESR1 is linked to breast cancer.