Preoperative GNAS and KRAS Testing in the Diagnosis of Pancreatic Mucinous Cysts

Management guidelines for pancreatic intraductal papillary mucinous neoplasms (IPMN) and mucinous cystic neoplasms (MCN) are based on the assumption that mucinous cysts can be accurately distinguished from other pancreatic cystic lesions. Previous studies using surgical material have identified recurrent mutations in GNAS and KRAS in pancreatic mucinous neoplasms. Yet, the diagnostic utility of testing for both genes in pancreatic cyst fluid obtained by endoscopic ultrasound-fine-needle aspiration (EUS-FNA) remains unclear. GNAS and KRAS testing was performed on EUS-FNA pancreatic cyst fluid from 91 pancreatic cysts: 41 IPMNs, 9 IPMNs with adenocarcinoma, 16 MCNs, 10 cystic pancreatic neuroendocrine tumors (PanNET), 9 serous cystadenomas (SCA), 3 retention cysts, 2 pseudocysts, and 1 lymphoepithelial cyst. Mutations in GNAS were detected in 16 (39%) IPMNs and 2 (22%) IPMNs with adenocarcinoma. KRAS mutations were identified in 28 (68%) IPMNs, 7 (78%) IPMNs with adenocarcinoma, and 1 (6%) MCN. Mutations in either gene were present in 34 (83%) IPMNs, 8 (89%) IPMNs with adenocarcinoma, and 1 (6%) MCN. No mutations were found in cystic PanNETs, SCAs, retention cysts, pseudocysts, and a lymphoepithelial cyst. GNAS and KRAS mutations had 100% specificity [95% confidence interval (CI), 0.83-1.00] but 65% sensitivity (95% CI, 0.52-0.76) for mucinous differentiation. Among IPMNs, mutations in either gene had 98% specificity (95% CI, 0.86-1.00) and 84% sensitivity (95% CI, 0.70-0.92). The combination of GNAS and KRAS testing was highly specific and sensitive for IPMNs; however, the lack of sensitivity for MCNs highlights the need for additional markers to improve the detection of pancreatic mucinous neoplasms.