POLK and cancer: In a deconstruction of whole-genome mutation datasets from the pan-cancer PCAWG database into all COSMIC v3.1 SBS signatures plus Signature 1C (now named Sig.POLKΔ, for POLK deficiency), the experimentally defined signature appeared as a minor component of a number of samples derived primarily from oesophageal and gastric cancer (Supplementary Figs. 5 and 6).