PTPN13 and stomach polyp: From an oncological point of view, it is well known that deletions involving the APC gene are associated with classical FAP1, mainly characterized by polyps and colorectal cancer, and attenuated FAP1, with extracolonic manifestations, including polyps of the stomach, osteomas, dental abnormalities, benign cutaneous lesions, desmoid tumors, and others [21].