Interestingly, alterations in expression of MMR proteins MLH1 and MSH2 have been reported in a variable proportion of NSCLC ranging from 18%4 to 61%,5 but no studies have investigated the role of reduced protein expression in precursor lesions of NSCLC and very few have investigated their potential prognostic significance in invasive carcinomas. This evidence concerns the gene MRC1 and non-small cell lung carcinoma.