Combination of dabrafenib plus trametinib for BRAF and MEK inhibitor pretreated patients with advanced BRAF-mutant melanoma: an open-label, single arm, dual-centre, phase 2 clinical trial.

Background: Patients with BRAF-mutant melanoma benefit from treatment with the combination of BRAF and MEK inhibitors, but resistance and disease progression develops in most patients. Preclinical studies and case studies have indicated that acquired resistance to BRAF inhibition can be reversible. We aimed to assess the anti-tumour activity of rechallenge with BRAF plus MEK inhibition in a prospective clinical trial.

Methods: In this open-label, single arm, dual-centre, phase 2 academic study in Belgium, patients aged 18 years or older with BRAF-mutant melanoma who had previously progressed on BRAF inhibitors (with or without MEK inhibitors) and were off-treatment for at least 12 weeks, were treated with dabrafenib 150 mg orally twice per day plus trametinib 2 mg orally once per day. The primary endpoint was the proportion of patients with investigator-assessed overall response at any time (defined as complete response or partial response according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 confirmed on two occasions, at least 28 days after the first response was recorded). Analyses were done in the intention-to-treat population. The study is ongoing but no longer recruiting patients. This trial is registered with ClinicalTrials.gov, number NCT02296996.

Findings: Between April 5, 2014, and Feb 2, 2016, 25 patients were enrolled and initiated treatment in our study. A partial response was documented in eight (32%) of 25 patients (95% CI 15-54; six patients had progressed on previous treatment with dabrafenib plus trametinib and two patients had progressed on previous BRAF inhibitor monotherapy). Stable disease was noted in ten patients (40%; 95% CI 21-61). Rechallenge with dabrafenib plus trametinib was well tolerated. There were no unexpected or grade 4 or 5 treatment-related adverse events. Grade 3 adverse events occurred in two patients (8%; panniculitis [n=1] and pyrexia [n=1]). Serious adverse events which occurred on study were one patient with an Addison crisis triggered by grade 2 pyrexia symptoms that resolved after discontinuation of dabrafenib and trametinib. No patients died as a result of study treatment.

Interpretation: Rechallenge with dabrafenib plus trametinib showed anti-tumour activity in patients who had previously progressed on BRAF inhibitors and as such, rechallenge represents a potential new treatment option for these patients.

Funding: Vlaamse Liga Tegen Kanker, Novartis.