POLE and gastric cancer: Three signature classes were mainly observed in the cohort: clock-like signatures (single-base substitution (SBS) 1 and 5), which were reported to have a high-prevalence in various cancer types, including gastric cancer [34–36] and polymerase epsilon exonuclease domain mutations (SBS10b), which are predominantly composed of C > T mutations and associated with a DNA polymerase epsilon (POLE) mutation in colorectal, endometrial, and gastric models [37].