The Indirect Efficacy Comparison of DNA Methylation in Sputum for Early Screening and Auxiliary Detection of Lung Cancer: A Meta-Analysis
NSCLC rates among the most frequent and lethal neoplasm world-wide and a significant decrease in morbidity and mortality relies only upon effective early diagnostic strategies. We investigated K-ras mutations and p16(INK4A) hypermethylation in tumor tissue and sputum of 50 patients with NSCLC and correlated them with sputum cytology and with tumor staging, grading and location, to ascertain, in sputum, their potential diagnostic impact. The same genetic/epigenetic abnormalities and cytological features were also evaluated in sputum from 100 chronic heavy smokers. Genetic analysis identified molecular abnormalities in 64% tumors (14/50 K-ras mutations and 24/50 p16(INK4A) hypermethylation) and in 48% sputum (11/50 K-ras mutations and 16/50 p16(INK4A) hypermethylation). In tumors K-ras mutations and p16(INK4A) hypermethylation were mostly mutually exclusive, being found in the same patients in 3 cases only. Genetic abnormalities in sputum were detected only in molecular abnormal tumors. Molecular changes in sputum had rates of detection similar to cytology (42%) but the cyto-molecular combination increased the diagnostic yield up to 60%. Interestingly, the rate of detection of genetic changes in sputum of tumors at early stage (T1) was not significantly different from that of tumors at more advanced stage (T2-T4). In fact K-ras point mutations were frequently recognised in tumors at early stage while p16(INK4A) inactivation prevailed in tumors at advanced stage ( P=0.0063). As expected, diagnostic cytological findings were more frequently found in tumors at advanced stage (P=0.004). No correlation was found between tumor grading and location (central versus peripheral) and molecular changes. p16(INK4A) hypermethylation, but not K-ras mutations, was documented in sporadic cases of asymptomatic heavy smokers (4%) where it was uncoupled from cytological abnormalities. In conclusion the cyto-molecular diagnostic strategy adopted in this study was able to detect the majority of tumors but in order to be proposed as effective and early diagnostic tool, this molecular panel needs to be tested in prospective studies with adequate follow-up.