These results suggest that GPDACs arise from small branch pancreatic ducts around accessory pancreatic duct penetrating the groove and duodenum and are distinguishable from DACs. Molecular immunohistochemistry suggests the accumulation of genetic abnormalities during tumor progression is slow in comparison with cPDACs. Thus, the site of PDAC occurrence, such as the border or inner area of the pancreas head, may determine genetic progressivity.