PLK1 and cancer: Despite Plk1's reputation as an essential protein for cell survival, Plk1 inhibitors are well tolerated by patients (Nokihara et al, 2016; Pujade‐Lauraine et al, 2016; Schoffski et al, 2012, 2010; Sebastian et al, 2010; Stadler et al, 2014; Van den Bossche et al, 2016) and there are diverse biological responses to Plk1 inhibition or knockdown in cancer cells (Choi et al, 2015; Craig et al, 2014; Driscoll et al, 2014; Gjertsen & Schoffski, 2015; McCarroll et al, 2015; Medema et al, 2011; Rudolph et al, 2009; Spankuch‐Schmitt et al, 2002).