P1.01-037 Circulating Tumor DNA Clearance During Treatment Associates with Improved Progression-Free Survival

Therapeutic selection has been shown to lead to marked clonal evolution, thus revealing limitations in imaging scan as a monitoring method, which does not reflect biological processes at a molecular level. However, currently, response assessment of patients with non-small cell lung cancer (NSCLC) primarily relies on imaging scans, necessitating the development of methodologies for dynamic monitoring of treatment response. We evaluated ctDNA as a tumor clonal response biomarker. We screened 831 advanced NSCLC patients with a mixture of prior treatment exposure by performing capture-based ultra-deep targeted sequencing on plasma samples using a panel consisting of 168 NSCLC-related genes. Eighty-six patients with driver mutations and a minimum of 2 evaluation points in addition to baseline were included for further analysis. At baseline, 79.9% patients harbored at least one mutation from this panel; the remaining 20.1% had no mutation detected. Sixty-nine percent of patients (570/831) harbored driver mutation. Patients harboring 2 mutations or fewer at baseline had a median progression-free survival (PFS) of 7.4 months; in contrast, patients harboring more than 2 mutations had a median PFS of 3.8 months (P=6.6x10-5 HR=0.34), suggesting a significant inverse correlation between number of mutations at baseline and PFS. Next, we evaluated the ability of ctDNA as a tumor clonal response biomarker in 86 patients with a minimum of 2 follow-ups. After a median follow-up of 314 days, 64 patients (74.4%) reached disease progression. During treatment, 46 patients, treated with either matched targeted therapy (MTT) or chemotherapy, had a minimum of one time of ctDNA clearance, occurring from 1.6 months to 7.5 months after the commencement of treatment, with a median PFS of 8.07 months, an overall response rate (ORR) of 41% and a disease control rate (DCR) of 93%. Median overall survival (OS) for this group has not reached. In contrast, 40 patients who had consistent detectable ctDNA throughout the course of treatment had a median PFS of 3.47months, a median OS of 425 days, an ORR of 20% and a DCR of 53%. Our data revealed that patients with a minimum of one time ctDNA clearance are associated with a better ORR (p=0.05), DCR (p=5.9x10-5), a longer PFS (p=5.4x10-10 HR=0.21) and OS (p=2.3x10-5 HR=0.21), regardless the type of treatment commenced and the time of evaluation. This real world study comprising a heterogeneous population reveals the predictive and prognostic value of ctDNA and warrants further investigations to explore its clearance as a surrogate endpoint of efficacy.