Serial circulating tumor DNA identification associated with the efficacy and prognosis of neoadjuvant chemotherapy in breast cancer.

Background: Circulating tumor DNA (ctDNA) provides a promising noninvasive alternative to evaluate the efficacy of neoadjuvant chemotherapy (NCT) in breast cancer.

Methods: Herein, we collected 63 tissue (aspiration biopsies and resected tissues) and 206 blood samples (baseline, during chemotherapy (Chemo), after chemotherapy (Post-Chemo), after operation (Post-Op), during follow-up) from 32 patients, and preformed targeted deep sequencing with a customed 1021-gene panel.

Results: As the results, TP53 (43.8%) and PIK3CA (40.6%) were the most common mutant genes in the primary tumors. At least one tumor-derived mutation was detected in the following number of blood samples: 21, baseline; 3, Chemo; 9, Post-Chemo; and 5, Post-Op. Four patients with pathologic complete response had no tissue mutation in Chemo and Post-Chemo blood. Compared to patients with mutation-positive Chemo or Post-Chemo blood, the counterparts showed a superior primary tumor decrease (median, 86.5% versus 54.6%) and lymph involvement (median, 1 versus 3.5). All five patients with mutation-positive Post-Op developed distant metastases during follow-up, and the sensitivity of detecting clinically relapsed patients was 71.4% (5/7). The median DFS was 9.8 months for patients with mutation-positive Post-Op but not reached for the others (HR 23.53; 95% CI, 1.904-290.9; p < 0.0001).

Conclusions: Our study shows that sequential monitoring of blood ctDNA was an effective method for evaluating NCT efficacy and patient recurrence. Integrating ctDNA profiling into the management of LABC patients might improve clinical outcome.

Trial Registration: This prospective study recruited LABC patients at Peking Union Medical College Hospital (ClinicalTrials.gov Identifier: NCT02797652).