POU4F1 and breast cancer: Furthermore, previous studies have shown that the POU3F2 (BRN2), one member of the POU domain family, can increase anoikis resistance in melanoma [38] and the POU4F1 reduces the resistance to trastuzumab by activating the mitogen-activated or extracellular signal-regulated protein kinase kinases 1 and 2 (MEK1/2) and extracellular-regulated kinase 1/2 (ERK1/2) signaling in HER2-positive breast cancer [39].