MYC and breast cancer: Zhang et al. used an autochthonous breast cancer model generated by overexpressing polyomavirus middle tumor antigen (PyMT) with or without MYC overexpression (MYC-PyMT vs. Control-PyMT) to study how the winner state of MYChi cells being regulated.1 They found that MYC accelerated the malignant tumor phenotype, featured by high numbers of large MYChi cancer cells closely adjacent to the apoptotic MYClo cancer cells, indicating the existence of cancer cell competition.