Stratification of patients by histological subtype revealed that young patients with mucinous adenocarcinomas of the appendix had 65% decreased odds of nonsilent variations in GNAS (OR, 0.35; 95% CI, 0.15-0.79; P = .01) compared with late-onset cases in adjusted models (eTable 3 in the Supplement). This evidence concerns the gene GNAS and mucinous adenocarcinoma of the appendix.