MKI67 and neoplasm: Next, we investigated three candidate evofosfamide sensitivity genes in our PDX models: the one electron reductase POR [59] that can convert evofosfamide into its active form [53], the endoribonuclease SLFN11, which plays a major role in sensitivity to DNA damaging agents [60,61,62], and a marker of proliferation, MKI67. There was moderate expression of MKI67 and POR across the PDX tumour models, but low expression of SLFN11 (Figure 5A).