Protein levels of GPX4, SLC7A11, and SLC3A2 in four luminal breast cancer cell lines (MDAMB415, ZR75-1, MCF7, and CAMA1), four basal breast cancer cell lines (MDAMB436, MDAMB231, HCC1937, and HCC1806), and one normal breast epithelial cell line (MCF10A) were concordant with mRNA expression (Supplementary Fig. 1b, c). This evidence concerns the gene SLC3A2 and breast cancer.