Clinical Significance Of Circulating Tumor DNA Detection In HER2 Positive Advanced Breast Cancer Patients Treated With Target Therapy

Objective:To investigate the effect of circulating tumor DNA on prediction of prognosis and disease monitoring in HER2 positive advanced breast cancer patients treated with target therapy, to explore tumor clone dynamics and its relationship with the therapy efficacy.Method:18 patients from the clinical trial BLTN-1b were recruited. All of the patients are diagnosed as HER2 positive advanced breast cancer and have signed the informed consent. In this clinical trial, they received an irreversible EGFR/HER2 targeted tyrosine kinase inhibitor monotherapy. Drug was administrated every morning by oral until the patient was assessed as "progression disease", withdrew her consent or showed unacceptable toxicity, or investigators had to terminate the trial. We collected baseline blood sample by venipuncture before the therapy started. Serial blood samples were collected at intervals of 56±3 days (28-day standard cycle for this drug). On the first and 28th day during drug administration, we collected blood samples every one or more hours. Imaging test was performed to document response to treatment according to the Response Evaluation Criteria in Solid Tumors(RECIST), version 1.1. Plasma was separated from the whole blood, plasma DNA was subjected to target hybrid capture next-generation sequencing. Single nucleotide variants(SNV), small insertion and deletion(indel) and copy number variants(CNV) in plasma circulating tumor DNA were identified. The study assessed disease-free survival of patients with different aberration number using the Kaplan-Meier method, survival differences were estimated using the log-rank test by SPSS22.0. Circulating tumor DNA from serial blood samples were used to track disease progression, showed in graphs plotted by software EXCEL. We identified mutation clusters using PyClone and showed clonal dynamics in patients with different responses to the treatment.Result:Sum of gene mutation and copy number variants is defined as aberration number. Mean and median progression-free survival are 17.3 and 8 weeks for patients whose baseline aberration number is more than five. Mean and median progression-free survival are 50.7 and 31.6 weeks for patients whose baseline aberration number is not more than five. Mean and median progression-free survival are 20.4 and 15.7 weeks for patients whose total aberration number is more than five. The mean progression-free survival are 73.9 and 77.7 weeks for patients whose total aberration number is not more than five. Survival analysis demonstrated that aberration number more than five was associated with inferior progression-free survival in patients with baseline or total aberration number differences, p=0.037 and p=0.023 respectively.For early-progression group, in which the six patients were assessed as "progression disease" at first follow-up, serial circulating tumor DNA analysis can track disease progression in five of them. For late-progression group, in which the six patients were assessed as "progression disease" after at least three follow-up assessments, the change of serial circulating tumor DNA reflected disease progression in all of them, and in three of them it showed a lead time of eight weeks over clinical disease progression.Circulating tumor DNA level increased in hours after drug administration in both early-progression and late-progression group. Circulating tumor DNA mutation clusters reflected the death and following DNA release of tumor cells sensitively. Circulating tumor DNA dynamics by hour is with great range and complexity.Conclusion:1.Baseline and total aberration number of circulating tumor DNA is associated with progression-free survival in HER2 positive advanced breast cancer patients treated with target therapy, patients whose aberration number is larger than five are with inferior progression-free survival2.Serial circulating tumor DNA detection can monitor disease progression in HER2 positive advanced breast cancer patients treated with target therapy and has shown value in predicting disease progression compared with clinical examination.3.Circulating tumor DNA level will increase in hours after target therapy begins in HER2 positive advanced breast cancer patients.