POU4F1 and breast cancer: DNA methylation is the most common epigenetic alteration observed in tumors.[20] We first investigated DNA methylation state in the promoter region of POU4F1 in breast cancer patients and surprisingly found that high expression of POU4F1 was significantly correlated with DNA hypomethylation in the promoter region of POU4F1 in both TCGA and METABRIC cohorts (Figure 7A; Figure S7D,E, Supporting Information).