Possible risk factors: Helicobacter pylori-related atrophic gastritis; Common TP53 mutations; RB1 mutations virtually absent; TP53-wildtype cases may have MSI-H; higher frequency of APC mutations than pulmonary NECs, and lower frequency of KRAS and BRAF mutations than colonic NECs; monoclonal origin in cases with a non-NEC component / MiNEN (sharing altered p53 pathway or MMR defect). Here, KRAS is linked to medical procedure.