Serial circulating tumor DNA analysis indicating the efficacy and prognosis of neoadjuvant chemotherapy for locally advanced breast cancer.

e12089 Background: The efficacy evaluation of neoadjuvant chemotherapy (NCT) for locally advanced breast cancer (LABC) is still a questionable issue. The clinical imaging is always discrepant from pathological assessment postoperatively, and conventional tumor markers, such as CEA and CA15-3, did not show significantly correlation with the response to NCT in breast cancer patients. Analysis of circulating tumor DNA (ctDNA) from blood may provide a promising alternative. Methods: Collectively, 63 tissue and 204 blood samples from 32 patients with LABC were collected. There were four sampling nodes for blood collection: at baseline, during chemotherapy, after chemotherapy and after operation. Hybrid capture-based genomic profiling with a 1021-gene panel was carried out for both tissue and blood samples. Results: Totally, 151 somatic mutations were detected in tissue samples from 32 patients. TP53 (n = 14, 43.75%) and PIK3CA (n = 13, 40.63%) were the most recurrent mutant genes. Among 11 patients with HER2 overexpression, 10 (90.91%) carried ERBB2 amplification. All of 21 patients with normal HER2 present diploid ERBB2. The overall concordance between HER2 overexpression and ERBB2 amplification was 96.88%. At least one tissue mutation could be detected in blood collected at baseline for 21 patients, during chemotherapy for three patients, after chemotherapy for nine patients, and after operation for four patients. There was no tissue mutation in blood collected during and after chemotherapy for four patients reached pathologic complete response (pCR). The median of pathological tumor decrease in situ was 54.63% (17.07% to 98.04%) for patients with tissue mutations in blood collected either during or after chemotherapy, and 86.53% (7.69% to 98.04%) for patients without tissue mutation in both blood samples. Furthermore, the median number of pathologically involved lymph nodes was 3.5 (0 to 16) and 1 (0 to 9) for two patients cohort, respectively. All of four patients with tissue mutations in postoperative blood experienced distant metastasis during follow-up, while only 7.14% (2/28) of those without tissue mutation relapsed. The median DFS was 9.8 and 22.7 months, respectively (HR 26.14, 95% CI 1.161 to 588.5, p < 0.0001). Conclusions: Sequential genomic profiling of blood ctDNA can be used to evaluate the therapeutic efficacy of NCT, as well as the postoperative survival. This study highlights the feasibility of integrating ctDNA profiling into the clinical management for LABC undergoing NCT. Clinical trial information: NCT02797652.