P3.13-033 DNA Methylation of PTGER4 and SHOX2 in Liquid Biopsies Facilitates the Diagnosis of Lung Malignancy After Chest CT-Scan

Lung Cancer (LC) is the leading cause of cancer-related death worldwide. The Lung Cancer Screening Trial screened 26,723 patients via Low-Dose chest CT-scan. Screening results were positive in 24.2%, however 96.4% were false positive. Therefore, a biomarker helping to discriminate false positive from true positive screening results will limit unnecessary interventions. The aim of this study was to analyze the feasibility of the DNA methylation markers prostaglandin E receptor 4 gene (PTGER4) and short stature homeobox 2 gene (SHOX2) as potential biomarkers in liquid biopsies additional to CT-scan findings suspicious for LC. A total of 73 patients with a chest CT-scan suspicious for stage I-IIIA LC were included in this study. LC was histologically confirmed in 50 patients. In the remaining 23 patients benign diagnoses were established. Circulating cell-free DNA was extracted, bisulfite converted and purified from 3.5 ml plasma, using a commercially available kit. Triplicates of bisulfited DNA were assayed with a 45-cycle rtPCR assay detecting methylated DNA of SHOX2, PTGER4 and ACTB as reference assay. Assay result was called positive for PTGER4 if at least two out of three PCR results had cycle threshold (Ct) values below 45; for SHOX2 if the Ct value was below 35. PCR-results were valid in 18 (4 organizing pneumonias, 5 pneumonias, 3 post-pneumonic residues, 3 hamartochondroma, 1 mycosis, 1 coal-workers pneumoconiosis, 1 aspergilloma) of 23 benign samples (control), and in 43 of 50 LC samples. PTGER4 results were negative in all controls and positive for 18 of 43 LC. These results translate into a specificity of 100 % and a sensitivity of 41.86% for LC detection via PTGER4. The SHOX2 assay was negative in all controls and positive in 9 LC patients, resulting in a specificity of 100 % and a sensitivity of 20.93% for SHOX2. Overall 21 of 43 LC samples were positive in either PTGER4 or SHOX2 and all controls were negative for both measurements. In combination both markers showed a specificity of 100% and a sensitivity of 48.84%. This specificity would imply a positive predictive value of 100%, further validation in a larger cohort is required. DNA methylation of PTGER4 and SHOX2 was highly specific for patients with chest CT-scan findings suspicious for LC. This could help to identify high-risk patients, who should be directly transferred to tissue-based diagnostics, surgery or stereotactic radiation. In the other cases the next diagnostic step should be decided clinically.