The analysis of the publicly available databases of transcriptomes of breast cancer samples showed that GPX4 gene expression positively correlates with IGFBP6 gene expression (i.e. decreases with a decrease in IGFBP6 gene expression) in tumor samples from patients with ER+ breast cancer in 4 analyzed data sets (in total 10 datasets of ER+ breast cancer were analyzed) and in 5 datasets of ER-breast cancer patients (in total 7 datasets of ER-breast cancer were analyzed). Here, GPX4 is linked to breast cancer.