Phase II Clinical Trial of Trametinib and Low-Dose Dabrafenib in Advanced, Previously Treated Wild-Type Melanoma (TraMel-WT).

Purpose: Patients with / wild-type melanoma who progress after immune checkpoint inhibitors (ICIs) have a poor prognosis. MEK inhibition has shown activity in this patient population but is associated with treatment-limiting skin toxicity. Combining a BRAF inhibitor with a MEK inhibitor is associated with less skin toxicity.

Methods: This phase II trial investigated trametinib (2 mg once daily) in patients with advanced / wild-type, ICI-refractory melanoma. In case of treatment-limiting skin toxicity, low-dose dabrafenib (50 mg twice daily) was added to trametinib. After a trial amendment, both drugs were combined up-front. The confirmed objective response rate (cORR) served as the primary end point.

Results: Twenty-four patients were included (50% male; median age 57 years; 92% Eastern Cooperative Oncology Group Performance Status 0-2; 75% stage IV-M1c/stage IV-M1d; median number of prior therapies: two [range, 1-5]). Three patients were enrolled before and 21 patients after the amendment, respectively. Seven confirmed and one unconfirmed partial responses (PRs) were observed (cORR, 29.2%). The median duration of response was 16.6 weeks (95% CI, 5.5 to 27.7). Stable disease (SD) was the best response in an additional five patients. Among the responding patients, genetic alterations causing mitogen-activated protein kinase (MAPK) pathway activation were documented in six patients. The disease control rate in patients with MAPK pathway-activating alterations was 64.3% (five confirmed PR, one unconfirmed PR, and three SD). The median progression-free survival was 13.3 weeks (95% CI, 3.5 to 23.1), and the median overall survival was 54.3 weeks (95% CI, 37.9 to 70.6). Adding low-dose dabrafenib to trametinib effectively mitigated or prevented treatment-limiting trametinib-related skin toxicity.

Conclusion: The combination of trametinib plus low-dose dabrafenib demonstrated encouraging efficacy and effective mitigation of skin toxicity in patients with advanced, ICI-pretreated / wild-type melanoma patients. MAPK pathway-activating alterations hold promise as a predictive biomarker.