Recent studies support that both enzymatic and nonenzymatic functions of PRC1 core components, especially BMI1 and RING1B, are critically involved in the development and progression of various tumor types.[7] In particular, BMI1 is overexpressed in many different types of cancer including breast,[8] lung,[9] and blood cancer.[10] RING1B is also highly involved in breast cancer malignancy[11] and leukemia progression.[12] Therefore, targeting PRC1 core components could provide a potential therapeutic approach for treating cancers with alterations in PRC1 components. Here, BMI1 is linked to breast cancer.