Analysis Of The Application Of Clonal Evolution Of Tumor In The Treatment Of Advanced Gastric Cancer By Using CtDNA Detection

Research background and objective: Gastric cancer(GC)is the fourth most common malignant tumor in the world,and the gastric cancer mortality ranks the second in the world.China is one of the regions with the highest incidence of gastric cancer.The incidence and mortality of gastric cancer among all types of cancers still rank among the top three in China.The early onset of gastric cancer is relatively insidious.The diagnosis is also difficult.It is prone to recurrence and metastasis,and lacks effective treatment for patients with advanced stage.Methods: This study included patients with advanced gastric cancer who had relapsed or were initially treated.The plasma ct DNA of the patients were collected and tested before the treatment and every 3 cycles of treatment evaluation.The paraffinembedded tissues and ascites from primary tumors or metastases were collected.At baseline and at the end of each treatment cycle(s),the efficacy evaluation(using RECIST v1.1 standard)was completed through CT or MRI scanning.The study endpoint of the study was progression-free survival(PFS).The next generation sequencing(SNV)technique was used to detect somatic mutations and germline mutations in 1021 tumor-related genes in ct DNA.Hybridization was applied to capture high-throughput sequencing to detect single nucleotide variants(SNV),insertions and deletions(In Del),copy number variants(CNV)and structural variation(SV).The molecular tumor burden(m TBI)was calculated by using the maximum allele mutation frequency(m VAFs)of the main cloning.By using clustering methodology and with the assistance of the Py Clone software the allelic mutations was analyzed,the evolutionary tree of clones was constructed and the evolution of tumor clones was analyzed.Results: A total of 125 samples were collected from 49 patients,including 108 plasma samples,11 tissue samples and 6 thoracic ascites samples.The baseline plasma ct DNA mutation detection rate was 83.67%(41/49),and at least one coincident mutation could be detected in 13 of 14 patients(13/14,92.9%)with plasma and tissue/astasis pairing.Baseline plasma m TBI was statistically significantly negatively correlated with PFS(Spearman correlation,P=0.0003,r= ﹣ 0.6522).High levels of baseline m TBI increased the risk of disease progression.In addition,m TBI showed a trend of dynamic changes parallel to the disease.Changes in plasma ct DNA before and after treatment could predict chemotherapy efficacy.Continuous dynamic monitoring of changes in plasma ct DNA could improve the accuracy of prediction.PFS was poorer in patients with new mutations(P=0.0472).PFS was significantly shorter in the new mutations group than in the no mutant group.The mutation spectrum of plasma ct DNA and tissue biopsy samples,ascites samples are highly matched.Amplification and deletion of CNV were significantly correlated with PSF(P=0.0001),and copy number variation increased the risk of tumor progression to metastasis.The target gene detected in this study was 103 samples,of which 21 samples were TMB-H(21/103,20.4%),3samples were MSI-H(3/103,2.9%),and 3 samples of MSI-H were also TMB-H(3/3,100%);MSI-H samples accounted for 14.3%(3/21)of TMB-H samples;TMB may be used more extensively than d MMR and MSI.Patients with a TMB ≥8 Muts/Mb were decided into the high TMB(TMB-H)group and patients with a TMB <8 Muts/Mb into the low TMB group(TMB-L).In a multivariable analysis,the PFS of baseline plasma TMB-H patients was not significantly different from that of TMB-L patients(P=0.0002),and the mean PFS of baseline TMB-H patients was lower than that of TMB-L patients.Clonal analysis can reflect the changes in molecular characteristics during tumor progression metastasis and drug therapy,which can be used to explore the clonal evolution of tumors.Conclusion: Patients with m TBI with high levels of baseline plasma ct DNA are at significantly increased risk of disease progression;m TBI shows a trend of dynamic changes parallel to the disease.Patients with new mutations have significantly shorter disease free survival during tumor therapy,and new mutations can lead to tumor resistance and progression.Copy number variation are high risk factors for tumor progression in patients with advanced gastric cancer.