To determine cut-points for ER and PR positivity based on the ESR1 and PGR mRNA data, we fit a mixture of two Gaussians to the ESR1 mRNA data and PGR mRNA data (separately), which produced a positivity cut-point of −1.3 for ESR1 and 0.4 for PGR. Based on these cut-points, we classified each of 3,666 cancers as ER+ (2,505; 68%) or ER- (1,161; 32%) based on mRNA expression levels. The gene discussed is ESR1; the disease is cancer.