Durable Complete Response of a Recurrent Mesencephalic Glioblastoma Treated with Trametinib and Low-Dose Dabrafenib in a Patient with Neurofibromatosis Type 1

Patients with neurofibromatosis type 1 (NF1) have an increased lifetime risk for the development of nervous system tumors, including high-grade gliomas (glioblastoma). NF1 is associated with the loss of expression of neurofibromin 1 (NF1 gene product). This hyperactivates the mitogen-activated protein kinase pathway, leading to cellular proliferation and survival. MEK-inhibitor monotherapy is a promising treatment strategy in this setting, but is associated with distinct adverse events, most prominently cutaneous toxicity. We report the case of a young NF1 patient with a recurrent, heavily pretreated mesencephalic glioblastoma who was treated with the MEK-inhibitor trametinib (2 mg once daily). A partial response was documented, but unfortunately, he developed dose-limiting cutaneous toxicity (rash, paronychia). Based on interim results of a phase 2 trial in advanced BRAFV600 wild-type melanoma indicating that a low dose of the BRAF-inhibitor dabrafenib is able to counter trametinib-related cutaneous toxicity, dabrafenib 50 mg twice daily was added. The cutaneous adverse events gradually recovered after addition of dabrafenib to trametinib. The patient eventually achieved a durable complete response, has excellent tolerance of his treatment and remains fully active.