MSH2 and Neoplasm of the lung: A count of grossly visible (macroscopic) tumors on the surfaces of the lungs (>1 mm in diameter) indicated that both K-rasLA1/+ and K-rasLA1/+; Msh2−/− mice had significantly increased tumor burden compared to wt or Msh2−/− genotypes alone at both 60–90 and 90–120 days old time points, while Msh2−/− mice exhibited a very low frequency of lung tumor development at both time points (Fig. 1A).