APC and gastric adenocarcinoma and proximal polyposis of the stomach: Approximately 70% of FAP patients exhibit extraintestinal manifestations, such as Gardner syndrome (13), Turcot syndrome (14), or gastric adenocarcinoma and proximal gastric polyposis (GAPPS) (15), all associated with germline mutations in the adenomatous polyposis coli (APC) gene.