POU5F1P1 gene was classified as a highly homologous pseudo-gene of POU5F1. It has been reported that POU5F1P1 produces a protein with similar function to POU5F1 and that it is associated with prostate cancer [16,33], breast cancer [17] and colorectal cancer [19,20,21,22], whereas the association of POU5F1P1 with gastric cancer is poorly understood. This evidence concerns the gene POU5F1B and breast cancer.