We first compared the expression of xCT in four breast cancer cell lines, MCF-7, MDA-MB-231, Hs-578t, and HCC-1937, and we found that MDA-MB-231, Hs-578t, and HCC1937 cells had higher gene and protein expressions of xCT than MCF-7 cells (Figure 1A,B). This evidence concerns the gene SLC7A11 and breast carcinoma.