The Role Of Circulating Tumor DNA Dynamically Monitored By Next-Generation Sequencing In Predicting The Efficacy Of Pembrolizumab Monotherapy For Non-small Cell Lung Cancer

Purpose: In recent years,Pembrolizumab was widely used for metastatic programmed death-ligand 1(PD-L1)positive non-small cell lung cancer(NSCLC).However,evaluate the efficacy of immune-checkpoint inhibitors are commonly guided by tumor imaging.Circulating tumor-derived DNA(ct DNA)can be used to monitor cancer dynamics noninvasively,and was proved as a biomarker for monitoring response to targeting therapy.In this study,dynamic monitoring of ct DNA was performed to investigate its association with the efficacy and drug resistance of Pembrolizumab monotherapy for advanced NSCLC.Methods: A total of 9 patients with advanced NSCLC in Northern Jiangsu People's Hospital from April 2016 to June 2018 were collected,who were epidermal growth factor receptor(EGFR),anaplastic lymphoma kinase(ALK)negative,and PD-L1 positive,defined as Tumor Proportion Score(TPS)?1%.All patients received Pembrolizumab(2mg/kg)monotherapy,administered every three weeks.We performed mutation profiling using targeted next-generation sequencing(a 425-cancer-gene panel)at baseline,3 weeks,6 weeks,and resistance weeks after treatment.Tissue tumor mutation burden(t TMB)and blood tumor mutation burden(b TMB)were calculated at baseline.At baseline and every nine weeks after treatment began to conduct a computed tomography(CT),changes in tumor size were compared to evaluate the efficacy,and the efficacy was evaluated by progression-free survival(PFS).PFS is defined as the time between the beginning of treatment to the onset of progressive disease(PD)or death for any cause.Results: 1.During the treatment period,Response Evaluation Criteria in Solid Tumors,version 1.1,all patients were evaluated for tumor efficacy every 9 weeks,among which4 patients(44%)were evaluated as partial response(PR),2 patients(22%)as stable disease(SD),3 patients(33%)as progressive disease(PD),and objective response rate(ORR)was 44%.The median progression-free survival was 4 months(95% CI: 2.5 to5.5 months).The median follow-up was 20 months(range,3 to 38).2.We sequenced genes from paired baseline tissue and plasma of 5 patients,and found the consistency between the detected molecular alterations in plasma and tumour was up to 65%(37/57).Thus,to a large extent,plasma specimens could be a complement or alternative for tissue samples in gene mutation analysis.Spearman correlation analysis showed a certain correlation between b TMB and t TMB(r=0.45).Patients with PFS<3 months had the lowest TMB,while patients with PFS>3 months had a relatively high TMB.With the increase of PFS,b TMB tends to increase gradually.3.There are two patients with PFS> 8 months,the mutant allele frequency(MAF)in ct DNA continued to decrease at 3and 6 weeks;while in 5 patients with PFS?4m,MAF showed an increasing trend at 3and 6 weeks.When resistance occurs,some acquired drug resistance mutations will occur subsequently,and the MAF in ct DNA keeps increasing.Patients who had traditionally evaluated partial response(PR)at week 9,or whose optimal efficacy was SD> 6 months,had a gene MAF in ct DNA approximately?1% found as early as week 6.However,patients whose CT efficacy was stable disease(SD)at 9 weeks and subsequently progressed,the 6-week ct DNA MAF was more than 1%.Conclusions: 1.b TMB level was related to PFS length of Pembrolizumab monotherapy.2.Changes of gene MAF in ct DNA can also predict sensitivity and resistance.As a sensitive biomarker to moniter the immunotherapy response of patients with NSCLC,ct DNA has shown enormous promise.