AFF1 and acute leukemia: PLK1 has been implicated in a number of acute leukemias (Bhojwani et al., 2006; Chow et al., 2017; Renner et al., 2009) and is expressed in a range of infant and pediatric ALLs, with levels being particularly high in samples from relapsed infants with MLL-AF4+ ALL (Figures 3D and 3E).