ctDNA SNORD3F Hypermethylation is a Prognostic Indicator in EGFR-TKI-Treated Advanced Non-Small Cell Lung Cancer

Purpose: DNA methylation plays a regulatory role in the oncogenesis and tumor progression and is valuable in the diagnosis and prognosis of cancer. While circulating tumor DNA (ctDNA) is widely used in the detection of oncogenic mutations and the guidance of treatment in advanced non-small cell lung cancer (NSCLC), studies of ctDNA methylation remains insufficient. We aim to investigate the methylation profiles of ctDNA in patients with advanced NSCLC undergoing EGFR-tyrosine kinase inhibitor (EGFRTKI) therapy and to discover novel biomarkers with predictive or prognostic value. Patients and Methods: We recruited 49 patients with EGFR-mutated advanced NSCLC undergoing EGFR-TKI as first-line treatment. Utilizing next-generation sequencing, we examined the somatic mutations and methylation signatures within the tumorassociated genomic regions of ctDNA from pre-treatment blood. Subsequently, we explored the association of these molecular features with the patients' response to therapy and their progression-free survival (PFS). Results: Genomic mutation profiling revealed no significant association of PFS or best overall response (BOR) and ctDNA status. Evaluation of ctDNA methylation showed a negative correlation between the methylation of small nucleolar RNA (snoRNA) genes and PFS (R=-0.31, P=0.043). Furthermore, high-level methylation of SNORD3F was associated with poorer PFS (mPFS 346d vs 243d, HR 0.49, 95% CI 0.24-0.93, P=0.029). Conclusion: Our study explored the prognostic value of ctDNA methylation in patients with advanced NSCLC undergoing targeted therapies and first revealed the predictive role of SNORD3F.