ESR1 and breast cancer: Compared to luminal (ER+) and HER2 overexpression tumors, basal breast cancer tumors expressed higher levels of metallothioneins, ZIP4 and ZIP14 genes and lower levels of ZIP6, ZIP9 and ZIP11. 142 Luminal breast cancer tumors express higher levels of the ZIP6 gene compared to basal and HER2 overexpression tumors, and ZIP8 gene expression is greater in high-grade versus low-grade ER+ tumors.142 Similarly, gene and protein expression profiles for zinc transporters have been assessed in luminal and basal breast cancer cell lines.