Since pathologically classified ERα+ breast cancers have been shown to express varying levels of ERα both at the protein and mRNA level, we examined the dataset from van de Vijver et al. [14] of 295 patient breast tumor mRNA expression profiles, focusing first on the subset of 226 ERα+ tumor profiles to determine whether E2-regulated genes might be correlated with ERα expression in these tumors. This evidence concerns the gene ESR1 and neoplasm.