Analysis Of Circulating Tumor DNA Monitors Anti-cancer Therapeutic Response In Metastatic Breast Cancer

Objective:We evaluated the feasibility of predicting response to endocrine therapy by serial gene-panel circulating tumor DNA(ctDNA)sequencing in hormone receptor(HR)positive metastatic breast cancer.Methods:We retrospectively analyzed 30 HR positive metastatic breast cancer patients treated in Cancer hospital,Chinese Academy of Medical Sciences and Peking Union Medical College from January 2015 to August 2016.Blood sample were collected from these patients before the next endocrine therapy.ctDNA was assayed by gene-panel target-capture next-generation sequencing.All of samples were further subdivided into two groups based on the drug-resistant mutations including TP53/PIK3CA/mTOR/ERBB2/ESRl/FGFR1.Survival curves were estimated using the Kaplan-Meier method and comparison of these estimates was performed using log-rank test.Chi square test was used to compare the difference of the primary drug resistance rate between the mutant group and the non-mutant group.Results:There are 20 patients in mutant group and 10 patients in non-mutant group respectively.The median follow-up time was 3 months(range 1-19 months).The median PFS to the endocrine therapy in the mutant group and non-mutant group were 3.0 months and 5.0 months respectively.The 6 months PFS rate of the mutant group was significantly lower than that of the non-mutant group(10%vs 50%,X2=8.328,P=0.004).Eighteen patients were primary resistant to endocrine therapy in 20 mutant group patients and 5 patients were primary resistant to endocrine therapy in 10 non-mutant group patients.The difference of the primary resistance rate between these two group was significant(X2=5.963,P=0.026).Conclusions:These results indicate that detecting multiple drug-resistant mutations in ctDNA can predict the response of endocrine therapy in HR positive metastatic breast cancer patients.Purpose:Breast cancer is a highly heterogeneous disease.Tumor heterogeneity is one of the major causes of drug resistance of anti-cancer therapy.It is very important to understand the heterogeneity of breast cancer and form a clinical standard measuring tumor heterogeneity.Therefore,present study explored the feasibility of chosing the HER2 traget therapy according to tumor hterogeneity analysis based on circulating tumour DNA(ctDNA).Methods:In this study,we retrospectively analyzed somatic variants of 193 tumour-related genes in ctDNA using next-generation sequencing,and to evaluate tumour heterogeneity and monitor therapeutic response in 37 metastatic breast cancer patients treated with human epidermal growth factor receptor(HER)2 inhibitor only or plus capecitabine.Results:We identified 502 somatic Single nucleotide variants(SNVs),9 somatic insertions and deletions(InDels)and 59 somatic copy number variants(CNVs)in 86 plasma DNA samples.Mutation cluster analysis identified 61 mutation clusters in 37 patients,and the median number of mutation clusters was 3(range,1-14)based on somatic variants of 37 baseline ctDNA samples.Interestingly,patients with high heterogeneity,defined by mutation number more than median number of two mutation clusters,had a significantly shorter progression-free survival time(PFS)(HR,2.74;95%CI 1.10-6.83;P = 0.030).The median PFS of patients with tumors of higher versus lower than median heterogeneity was 30.0 weeks versus 60.0 weeks respectively.Furthermore,we found that the median PFS of those patients(7.8 weeks,95%Cl,7.4-26.8)with trunk resistance mutations was significantly shorter than those patients(31.6 weeks,95%Cl,15.7-60.0)with branch resistance mutations or without any resistance mutations in 17 patients treated by pyrotinib only.Moreover,we dynamically observed the change of percentage of clonal population in cell free(cfDNA)during treatment in 21 patients with serial of plasma samples.We found that different clonal population in plasma cfDNA of one patient had different response against the same treatment.Correlation analysis showed high positive correlation between mTBI(molecular tumour burden index)value calculated by ctDNA and tumour size measured by computed tomography(CT)(P<0.0001),while monitoring the mTBI in serial ctDNA increased sensitivity for prediction of progressive disease in 6 of 21 patients,with 8-16 weeks earlier than using CT scan.Comparing with CT scan,the sensitivity of mTBI were 81%(17/21)to predict the disease progression.Conclusions:Our current findings suggested that patients with high heterogeneity have a poor efficacy to anti-cancer therapies.Clonal structure analysis based on ctDNA could predict the therapeutic response to anti-cancer drugs.Serial ctDNA monitoring molecular tumor burden is highluy consistent with the burden assessed by imaging in clinical.