POU5F1 and breast cancer: In addition, transcription factors involved in stem cell self-renewal and pluripotency, such as POU class 5 homeobox 1 (POU5F1 [also known as OCT4]), NANOG homeobox (NANOG), and SRY (sex determining region Y)-box 2 (SOX2) proteins, have been shown to be up-regulated in human breast cancer, and their overexpression is linked to cell transformation, tumorigenicity, tumor metastasis, and distant recurrence following chemotherapy [11, 12].