The expression level of cancer stem cell phenotype regulator B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1), which is also a component of the polycomb repressive complex 1 (PRC1) and its transcription is dramatically regulated by Myc, is up-regulated in various cancers especially breast cancers (Dimri et al., 2015; Hiraki et al., 2017). Here, PRC1 is linked to cancer.