PTTG1 and cervical squamous intraepithelial neoplasia: Key regulators of cell cycle checkpoints, in particular those involved in the G2/M checkpoint (CDK1, CCNA2, CCNB1, CCNB2) and the mitotic checkpoints (AURKA, BUB1, BUB1B, CENPA, MAD2L1, NDC80, NEK2, PTTG1, TTK), were clearly over-expressed in high CIN samples.