The importance of differences in expression of reductases is evident particularly for PR‐104, where mRNA for the two‐electron reductase AKR1C3, which catalyses its metabolic activation independently of hypoxia [21], was more highly expressed in SiHa > UT‐SCC‐74B > HCT116/54C tumours, with very little to no expression in UT‐SCC‐16A (Fig. 4F). Here, AKR1C3 is linked to neoplasm.