TTK and breast cancer: Our laboratory has demonstrated that deregulation of regulators of the centrosome cycle, mitosis, and G1/S phase including Cdk4, the E2F activators (E2F1, E2F3a), Nek2, Sgo1, and Mps1/TTK are required to maintain high CA and CIN in Her2+ breast cancer cells [34, 62, 68].