Application of Methylation Markers in Early Detection and MRD Monitoring of Lung Cancer

Lung cancer has the highest global incidence and mortality among all malignancies. As a high-incidence country, China reported approximately 1.0606 million new cases and 733,300 deaths in 2022, accounting for 22.0% and 28.5% of all malignant tumors, respectively. While early surgery is the primary curative approach, the risk of postoperative recurrence is substantial, with 5-year recurrence rates of 19% for stage IA, 30% for stage IB, and 48.6% for stage II NSCLC. The 3-year recurrence rate for stage III patients is as high as 52%. Crucially, even when imaging confirms a "tumor-free status" (R0 resection), hidden minimal residual disease (MRD) often leads to recurrence.

Current MRD detection primarily analyzes mutations in circulating tumor DNA (ctDNA). However, high inter-patient mutational heterogeneity poses challenges for designing compact, broadly effective detection panels. The Tumor-informed approach, which designs patient-specific panels, is limited by its dependency on tumor tissue samples. In contrast, DNA methylation biomarkers for MRD analysis do not require prior knowledge of tumor-specific mutations. Their sensitivity is independent of high-frequency mutation burden, changes occur early in tumorigenesis, and they exhibit tissue and cancer type specificity. Furthermore, DNA methylation shows consistency across numerous genomic regions, enabling detection via multiple CpG sites.

The "Expert Consensus on Tumor DNA Methylation Biomarker Testing and Clinical Application (April 2024)" states that variations in DNA methylation levels are closely associated with tumor prognosis and can be used for MRD assessment and recurrence monitoring. Mounting evidence supports this: A 2023 BMC Medicine study of 195 NSCLC patients found that individualized methylation-based MRD monitoring signaled recurrence earlier than mutation-based monitoring. A 2023 JAMA Oncology study demonstrated that detecting ctDNA methylation of five genes could predict colorectal cancer recurrence up to 20 months earlier than imaging, with significantly higher recurrence risk in patients positive for ctDNA one month post-surgery (HR=17.5). Another prospective study (NCT00958737) in 805 colorectal cancer patients confirmed a significantly higher 2-year disease-free survival rate in the ctDNA methylation-negative group (82% vs 64%).

This study aims to investigate the role of plasma SHOX2 and PTGER4 gene methylation levels in monitoring MRD and evaluating efficacy in NSCLC patients post-surgery. The study will enroll patients with histopathologically/clinically diagnosed stage I-IV NSCLC undergoing surgical resection. Peripheral blood will be collected at multiple timepoints: pre-treatment, and post-treatment at 3 days, 1 month, 3 months, 6 months, 9 months, 12 months, 18 months, 24 months, and upon recurrence for ctDNA methylation analysis.

Statistical analyses will include: Assessing the correlation between methylation levels and radiological metrics using Pearson or Spearman coefficients; Evaluating the predictive power for recurrence using Receiver Operating Characteristic (ROC) curves; Stratifying patients into high-risk and low-risk groups based on methylation results; Plotting recurrence-free survival curves using the Kaplan-Meier method and comparing groups with the Log-rank test; Assessing the independent predictive value of SHOX2 and PTGER4 methylation for recurrence risk using multivariate Cox regression analysis, adjusting for confounders like age, gender, and tumor stage; Finally, evaluating individualized therapeutic efficacy based on the timing of ctDNA positivity, Disease-Free Survival (DFS), and Overall Survival (OS). The goal is to provide a scientific basis for predicting recurrence risk and guiding treatment decisions.