[DNA methylation detection of SHOX2 and PTGER4 in plasma contributes to differential diagnosis of pulmonary nodule patients].

Objective To investigate the clinical significance of plasma cell free DNA (cfDNA) methylation in short stature homeobox 2 (SHOX2) and prostaglandin E receptor 4 (PTGER4) for diagnosing pulmonary nodule patients. Methods We collected 10 mL venous blood from patients. And the plasma DNA was extracted. Real-time quantitative PCR was performed to amplify the DNA after bisulfite conversion. Valid Ct values were input into specialized software to analyze the methylation status of SHOX2 and PTGER4. Histological classification of lung malignant tissues was carried out by immunohistochemistry. Results The 22 of 57 patients were positive and 35 were negative for SHOX2 and PTGER4 DNA methylation detection. Computed tomography (CT) indicated that 31 of 57 patients were diagnosed with pulmonary nodules, among which 19 patients were positive for DNA methylation; 3 of 16 patients with inflammation on CT were positive for DNA methylation; 10 patients with normal or ground glass CT images were negative for DNA methylation. Significant differences in SHOX2 and PTGER4 DNA methylation were observed in the patients with different CT findings. The highest positive rate of CT nodular lesions was 61.3%. The 20 patients with pulmonary nodules were pathologically diagnosed with lung cancer, of which 18 were positive for SHOX2 and PTGER4 DNA methylation, with a positive rate of 90%. Only 1 case of benign pulmonary nodules was positive. Significant difference in SHOX2 and PTGER4 methylation status was observed between benign and malignant pulmonary nodules. The positive rate of SHOX2 and PTGER4 methylation were both 100% in squamous cell lung carcinoma and small cell lung carcinoma, while 75% in adenocarcinoma. Conclusion SHOX2 and PTGER4 methylation detection in blood plasma has certain value in the early diagnosis of lung cancer and can be a complementary tool of CT in diagnosing pulmonary nodule patients.