POU4F1 and breast cancer: DNA hypomethylation was frequently accompanied by accessible chromatin, which is a hallmark of active promoter.[21] Further analysis of the assay for transposase‐accessible chromatin using sequencing (ATAC‐Seq) of breast cancer patients showed that BLBC patients had higher chromatin accessibility in the POU4F1 promoter and there was a significant positive correlation between the POU4F1 expression and the intensities of the two ATAC‐seq peaks located in the transcription start site (TSS) region of POU4F1 in BLBC patients (Figure 7E,F).