PLK1 and cancer: PLK1 can contribute to CIN and therefore tumor heterogeneity through the dysregulation of mitotic entry by overriding mitotic checkpoints to drive cancer cells to mitosis before DNA replication has been properly resolved or DNA damage repaired, through dysregulation of centrosome duplication, maturation, and the formation of the mitotic spindle, through premature chromosome segregation by overriding the SAC, through improper chromosome segregation due to altered kinetochore dynamics, and through altered telomere function.