KRAS and adenoma: To investigate whether the level of pERK1/2 expression is influenced by Kras mutation status, the 24 adenomas and 13 adenocarcinomas were evaluated for grading of positive scores of single‐immunohistochemical staining for pERK1/2 (classified into four categories, negative (positive score 0), weak (positive score 1 and 2), moderate (positive score 3 and 4), and strong (positive score 6≤)) and Kras mutation status.