Proof-of-concept studies also suggested the use of ctDNA levels as a dynamic biomarker reflecting the tumor response to therapy in metastatic breast cancer patients. We previously reported that TP53 mutations can be detected in the plasma of most metastatic Triple Negative Breast Cancer (TNBC) patients. Yet, few data about ctDNA levels and changes during neoadjuvant chemotherapy (NCT) are available for localized breast cancer. We investigated whether circulating tumor DNA (ctDNA) detection can reflect the tumor response to NCT and detect minimal residual disease after surgery non-metastatic TNBC patients.
10 ml of plasma were collected at 4 time points: before NCT; after 1 cycle; before surgery; after surgery. Customized ddPCR assays were used to track TP53 mutations previously characterized in tumor tissue by massively parallel sequencing (MPS).
Forty-six patients with non-metastatic TNBC were enrolled. TP53 mutations were identified in 40 of them. Customized ddPCR probes were validated for 38 patients, with excellent correlation with MPS (r = 0.99), specificity (≥2 droplets/assay) and sensitivity (at least 0.1%). At baseline, ctDNA was detected in 27/36 patients (75%). Its detection was associated with mitotic index (p = 0.003), tumor grade (p = 0.003) and stage (p = 0.03). During treatment, we observed a drop of ctDNA levels in all patients but one. No patient had detectable ctDNA after surgery. The patient with rising ctDNA levels experienced tumor progression during NCT. Pathological complete response (16/38 patients) was not correlated with ctDNA detection at any time point. ctDNA positivity after one cycle of NCT was correlated with shorter disease-free (p
Customized ctDNA detection by ddPCR achieved a 75% detection rate at baseline. During NCT, ctDNA levels decreased quickly and minimal residual disease was not detected after surgery. However, a slow decrease of ctDNA level during NCT was strongly associated with shorter survival. If confirmed by further prospective studies, ctDNA may become a clinically valuable prognostic tool to manage TNBC patients treated by NCT.
Clinical trial identification
Legal entity responsible for the study
ITMO Santé Publique and SIRIC Institut Curie
All authors have declared no conflicts of interest.