POU5F1 and breast cancer: The relationship between YY1 and SOX2 expressions as well as the expressions of BMI1 and OCT4 resulted in the classification of four groups of cancers with distinct molecular signatures: 1) Prostate, lung, cervical, endometrial, ovarian and glioma cancers (YY1loSOX2hiBMI1hiOCT4hi) 2) Skin, testis and breast cancers (YY1hiSOX2loBMI1hiOCT4hi) 3) Liver, stomach, renal, pancreatic and urothelial cancers (YY1loSOX2loBMI1hiOCT4hi) and 4) Colorectal cancer, lymphoma and melanoma (YY1hiSOX2hiBMI1loOCT4hi).