PLK1 and cancer: Since both Plk2 and Plk3 are required for promoting cell survival (Burns et al. 2003; Xie et al. 2005) and they exhibit properties similar to tumor suppressors (Smith et al. 2006; Yang et al. 2008; Coley et al. 2012), specific inhibition of Plk1, but not Plk2 or Plk3, would be important for selectively killing cancer cells, but not normal cells.