Thus, a small quantity of ERα protein may be owing to TNBC heterogeneity26, and the low levels of ERα protein in few Tg-Neu tumors, which are well defined as ERα-negative, may have originated from the non-malignant or premalignant cells in the tumor mass27,28 (Supplementary Fig. 3e). This evidence concerns the gene ESR1 and neoplasm.