Despite decades of cancer research, the early phases of tumour progression that connect the appearance of few abnormal cells to the formation of a clinically detectable tumour mass remains poorly understood. It was previously proposed that certain mutations could give a competitive advantage to a subset of cells that would enable them to kill and replace their neighbours, thereby initiating a cancerous tumour. Yet, the mechanisms surrounding the basis of such competition were not clear. Researchers from the Institut Pasteur and the Champalimaud Centre for the Unknown, have just discovered a new mechanism that may explain how tumoural cells can eliminate their neighbours and spread throughout the body.