APC and neoplasm: The methylation status of five selected gene promoters (APC, RASSFIA1, FOXA1, SLFN11, SHOX2) was examined by highly specific and sensitive real-time methylation specific PCR assays in: (a) a training group of 35 primary tumors and their corresponding adjacent non-cancerous tissues of early stage NSCLC patients, (b) a validation group of 22 primary tumor tissues (FFPEs) and 42 peripheral blood samples of early stage NSCLC patients.