Molecular analysis of preoperative cyst fluid from the IPMN/MCN/PDAC group with 36 surgical specimens in total, showed at least one mutation in KRAS or GNAS genes in 31 (86.1%), including 16 of the 21 (76.2%) cases incorrectly classified by cytology (“NEG”: n = 9, “ND”: n = 7). The gene discussed is GNAS; the disease is cyst.