PMS1 and gastric cancer: All data related to the hypermutated cases can be found in Supporting Information File A. The most frequently mutated genes among the 10 patients with hypermutated GC tumors were KMT2C (70.0%), LRP1B (70.0%), and KMT2A/KMT2D/PMS1/TP53 (50.0%), with amplifications of ARNT, MCL1, CDX2, FOXO1, and SMARCB1 observed in 10% of the cases.