We used four tumor cell lines for this study: (1) the human breast cancer cell line MDA-MB-231 is OCT-4 positive and expresses the OCT-4 inducing leukemia inhibitory factor, LiF20; (2) the murine mammary carcinoma EMT-6 undergoes epithelial-mesenchymal transition; (3) the human pancreatic adenocarcinoma BxPC-3 has not, to our knowledge, been shown to express OCT-4 ; and (4) the murine breast cancer model 4T1luc is an aggressive tumor model with significant drug resistance. This evidence concerns the gene POU5F1 and breast cancer.