POU4F1 and neoplasm: TET1 has been reported to mediate aberrant hypomethylation in TNBC/BLBC and promote tumor progression.[28] We then used siRNA to silence TET1 in BT549, MDA‐MB‐231, and HS578T cells and found TET1 knockdown significantly enhanced the DNA methylation of POU4F1, leading to the downregulation of POU4F1 (Figure 7J,K; Figure S9D, Supporting Information).