Background: Adenocarcinoma of the pancreas is likely to spread into the nerve plexuses around the superior mesenteric artery (SMA) at a microscopic level. Since there has been no detailed report on how minute cancer invasion is distributed among the peri-SMA plexuses or which cases are more vulnerable to such an event, it has long been controversial how to treat this area when resecting the pancreatic head cancer. Hypothesis: The K-ras mutation assay is more sensitive than the conventional histologic diagnosis in detecting minute cancer invasion around the SMA.