GNAS and neoplasm: When analysis of fresh-frozen peritoneal tumor samples did not reveal mutations, macrodissected formalin-fixed samples were analyzed.<h4>Results</h4>Mutations in cancer-related genes were detected in 98 % of the analyzed samples, with <i>KRAS</i> and <i>GNAS</i> mutated in 148 (89 %) and 139 (83 %) cases, respectively.