A Phase 2 Clinical Trial of Trametinib and Low-Dose Dabrafenib in Patients with Advanced Pretreated Mutant Melanoma (TraMel-WT).

Background: MEK-inhibitor monotherapy has activity in advanced mutant melanoma but is associated with dose-limiting cutaneous toxicity. The combination of a BRAF- with a MEK-inhibitor at their full dose (as in mutant melanoma) has low cutaneous toxicity. It is unknown whether a low dose of BRAF-inhibitor can mitigate the skin toxicity associated with full-dose MEK-inhibitor treatment in patients with advanced mutant melanoma.

Methods: This two-stage phase 2 clinical trial investigated trametinib 2 mg once daily in patients with advanced mutant melanoma who were pretreated with immune checkpoint inhibitors. In case of trametinib-related cutaneous toxicity, low-dose dabrafenib (50 mg twice daily) was added to prevent recurrent cutaneous toxicity (pre-amendment). Following an amendment, trametinib was combined upfront with low-dose dabrafenib (post-amendment). Objective response rate (ORR) served as the primary endpoint.

Results: All 6 patients enrolled pre-amendment developed trametinib-related cutaneous toxicity, necessitating treatment interruption. Combining trametinib with low-dose dabrafenib prevented recurrent skin toxicity thereafter. Trametinib-related skin toxicity was effectively mitigated in all 10 patients post-amendment. In all 16 included patients, the ORR and disease control rate was 6.3% (1 partial response) and 50.0%, respectively. The trial was halted after the first stage.

Conclusions: Combining full-dose trametinib with low-dose dabrafenib can mitigate MEK-inhibitor-related skin toxicity but was insufficiently active in this patient population. This combination can be of further interest for the treatment of MEK-inhibitor-sensitive tumors.