ESR1 and breast cancer: We used VDX (a breast cancer microarray dataset introduced by Wang, Minn et al. [18,19]) as a training set since this population contained the largest sets of ER-/HER2- (99), HER2+ (54) and ER+/HER2- (191) tumors from node-negative patients who had not received any systemic treatment (referred to as 'untreated/').