POU5F1 and neoplasm: Interestingly, the tumour volume was increased in the OCT4‐induced MDA‐MB‐231 group compared with the control group, and the vast majority of subcutaneous tumours were strongly positive for Ki67 in the OCT4‐induced MDA‐MB‐231 group, indicating that OCT4 facilitated tumour formation of MDA‐MB‐231 cells (Figure 3A,B).