MRC1 and lung neoplasm: It results from germ-line mutations in MMR genes, with alterations of hMLH1 and hMSH2 accounting for the vast majority of cases.1 This syndrome is characterized by genetic instability and the propensity to develop a number of neoplasms, particularly colorectal cancer and, to a lesser extent, malignancies of the endometrium, stomach, pancreas, ureters, ovaries, brain and skin.3 Pulmonary neoplasms are not a characteristic feature of this syndrome, suggesting that defective MMR gene function may not play a major role in the pathogenesis of NSCLC.