ESR1 and neoplasm: In nine datasets containing both IHC-based ER positive and ER negative tumours, we observed a bimodal distribution of ESR1 expression, with coefficients of bimodality ranging from 0.619 to 0.776, whereas in the data set with only IHC ER negative tumours (JBI2) there was no visible bimodal distribution of ESR1 (coefficient of bimodality  = 0.412, Supplement Figure S1).