Further analysis of these cohorts and of targeted sequencing data from an additional series of endometrial cancers from the LUMC, including 32 POLE‐mutant tumours, confirmed the over‐representation of E → *, R → * and arginine to glutamine substitutions (R → Q) among POLE‐mutant cases, concordant with the results from the paired endometrial lesions and consistent with the known trinucleotide bias of the POLE mutational signature (supplementary material, Figures S8–S10 and Tables S7–S11). Here, POLE is linked to endometrial cancer.