We are, to our knowledge, the first to demonstrate that early-stage breast tumors with low-positive (1–9%) and intermediate-positive (10–50%) ER expression have more similarities in immune biology to TNBC than to their highly ER-positive counterparts, based on sTILs, CD8 + T-cell presence, PD-L1 expression and expression of immune pathways. This evidence concerns the gene ESR1 and breast neoplasm.