DNA Methylation Changes in Atypical Adenomatous Hyperplasia, Adenocarcinoma In Situ, and Lung Adenocarcinoma

BACKGROUND:Aberrant DNA methylation is common in lung adenocarcinoma, but its timing in the phases of tumor development is largely unknown. Delineating when abnormal DNA methylation arises may provide insight into the natural history of lung adenocarcinoma and the role that DNA methylation alterations play in tumor formation. METHODOLOGY/PRINCIPAL FINDINGS:We used MethyLight, a sensitive real-time PCR-based quantitative method, to analyze DNA methylation levels at 15 CpG islands that are frequently methylated in lung adenocarcinoma and that we had flagged as potential markers for non-invasive detection. We also used two repeat probes as indicators of global DNA hypomethylation. We examined DNA methylation in 249 tissue samples from 93 subjects, spanning the putative spectrum of peripheral lung adenocarcinoma development: histologically normal adjacent non-tumor lung, atypical adenomatous hyperplasia (AAH), adenocarcinoma in situ (AIS, formerly known as bronchioloalveolar carcinoma), and invasive lung adenocarcinoma. Comparison of DNA methylation levels between the lesion types suggests that DNA hypermethylation of distinct loci occurs at different time points during the development of lung adenocarcinoma. DNA methylation at CDKN2A ex2 and PTPRN2 is already significantly elevated in AAH, while CpG islands at 2C35, EYA4, HOXA1, HOXA11, NEUROD1, NEUROD2 and TMEFF2 are significantly hypermethylated in AIS. In contrast, hypermethylation at CDH13, CDX2, OPCML, RASSF1, SFRP1 and TWIST1 and global DNA hypomethylation appear to be present predominantly in invasive cancer. CONCLUSIONS/SIGNIFICANCE:The gradual increase in DNA methylation seen for numerous loci in progressively more transformed lesions supports the model in which AAH and AIS are sequential stages in the development of lung adenocarcinoma. The demarcation of DNA methylation changes characteristic for AAH, AIS and adenocarcinoma begins to lay out a possible roadmap for aberrant DNA methylation events in tumor development. In addition, it identifies which DNA methylation changes might be used as molecular markers for the detection of preinvasive lesions

Effects of dual-energy subtraction chest radiography on detection of small pulmonary nodules with varying attenuation: receiver operating characteristic analysis using a phantom study

Purpose: To investigate the detectability of simulated pulmonary nodules with different X-ray attenuation by flat-panel detector (FPD) chest radiography using a dual-exposure dual-energy subtraction (DES) technique.Materials and Methods: Using a FPD radiography system we obtained 108 sets of chest radiographs of a chest phantom. They consisted of 54 sets each of chest radiographs with- and without simulated nodules. Each data set contained a standard- and a corresponding dual-energy subtracted chest radiograph (DES image). The diameter of the simulated nodules was 8-, 10-, and 12 mm; nodules of each size manifested attenuation of -450, -200, and 30 Hounsfield units (HU). We performed receiver operating characteristic (ROC) analysis to compare the observers’ performance in detecting nodules.Results: For -450 HU nodules the mean area under the ROC curve (AUC) without and with DES images was 0.66 and 0.77, respectively; the difference was significant (paired t-test, p < 0.01). For nodules with -200- and 30 HU, there was no significant difference in the AUC value (0.79 vs. 0.77, p=0.13; 0.92 vs. 0.94, p=0.17, respectively).Conclusion: The addition of DES images to standard chest radiographs improved the performance of radiologists charged with detecting simulated nodules with an attenuation of -450 HU