SLC3A2 and cancer: As xCT activity was shown to drive the expression of the selenoprotein GPX4 via the selenocysteine biosynthesis pathway (Figure 1a, [4]), we examined the levels of SLC7A11, SLC3A2, and GPX4 in breast normal and cancer tissues to confirm if this pathway is altered in cancer tissues and if GPX4 expression is associated with the expression of xCT.