Results of the c-TRAK TN trial: a clinical trial utilising ctDNA mutation tracking to detect molecular residual disease and trigger intervention in patients with moderate and high-risk early stage triple negative breast cancer

Background: Post-treatment detection of circulating tumour DNA (ctDNA) in early-stage triple negative breast cancer (TNBC) patients predicts high risk of relapse. c-TRAK-TN assessed the utility of prospective ctDNA surveillance in TNBC and the activity of pembrolizumab in patients with ctDNA detected (ctDNA+). Patients and methods: c-TRAK-TN, a multi-centre phase II trial, with integrated prospective ctDNA surveillance by digital PCR, enrolled patients with early-stage TNBC and residual disease following neoadjuvant chemotherapy, or, stage II/III with adjuvant chemotherapy. ctDNA surveillance comprised three monthly blood sampling to 12 months (18 months if samples were missed due to COVID), and ctDNA+ patients were randomised 2:1; intervention:observation. ctDNA results were blinded unless patients were allocated to intervention, when staging scans were done and those free of recurrence were offered pembrolizumab. A protocol amendment (16/09/2020) closed the observation group; all subsequent ctDNA+ patients were allocated to intervention. Co-primary endpoints were i) ctDNA detection rate ii) sustained ctDNA clearance rate on pembrolizumab (NCT03145961). Results: 208 patients registered between 30/01/18 - 06/12/19, 185 had tumour sequenced, 171 (92·4%) had trackable mutations, and 161 entered ctDNA surveillance. Rate of ctDNA detection by 12 months was 27·3% (44/161,95%CI:20·6-34·9). Seven patients relapsed without prior ctDNA detection. 45 patients entered the therapeutic component (intervention n=31; observation n=14; 1 observation patient was re-allocated to intervention following protocol amendment). Of patients allocated intervention, 72% (23/32) had metastases on staging at time of ctDNA+, and 4 patients declined pembrolizumab. Of the five patients who commenced pembrolizumab, none achieved sustained ctDNA clearance. Conclusion: c-TRAK-TN is the first prospective study to assess whether ctDNA assays have clinical utility in guiding therapy in TNBC. Patients had a high rate of metastatic disease on ctDNA detection. Findings have implications for future trial design, emphasising the importance of commencing ctDNA testing early, with more sensitive and/or frequent ctDNA testing regimes