The epithelial cell cluster signature separation between ER+ (Cluster 2) and TNBC (Cluster 7, 9) was striking, supportive of the paradigm that the two subtypes of breast cancers may have originated from different cell types: ER+ tumors arising from luminal cells (Cluster 2) and TNBC tumors arising from basal cells (Cluster 7). This evidence concerns the gene ESR1 and breast cancer.