PDCD1 and breast cancer: By mass spectrometry analysis performed in a breast cancer stem cell model (human mammary epithelial HMLER CD24low/CD44high) [19], salinomycin, a ferroptosis inducer [44], was capable of inducing protein upregulation of CD274 and TNFAIP3 (Figure 4D,E) without any modulation of PDCD1.