Therefore, we sought to determine whether COX-2 deletion affects the incidence of bronchial hyperplasia, bronchial adenoma, and/or bronchial carcinoma in mice carrying mutant KRAS. Histopathological analysis demonstrated that the lung tissues of K-ras mice had significantly more bronchioalveolar hyperplasia than did lung tissues of K-ras/COX-2−/− mice. Here, PTGS2 is linked to hyperplasia.