Using metastatic hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2−) breast cancer cells, Pottier et al. revealed that the protein expression of GPX4 was increased in parental cells (e.g., CAMA1, T47D, and ZR75.1) after treatment with a palbociclib and fulvestrant (PF) combination, and in PF-resistant cells (e.g., CAMA1-PFR, T47D-PFR, and ZR75.1-PFR). This evidence concerns the gene HR and breast carcinoma.