Regression of BRAF V600E mutant adult glioblastoma after primary combined BRAF-MEK inhibitor targeted therapy: a report of two cases

Up to 15% of young adults with glioblastoma have the activating oncogenic mutation, an actionable target of the MAPK signal transduction pathway governing tumor cell proliferation. Small molecule inhibitors of BRAF and MEK, a downstream protein immediately following BRAF, have been shown to confer a survival advantage for patients with mutant advanced melanoma. We describe our experience using this combined target therapy for two patients with BRAF mutant glioblastoma (GBM) as primary treatment due to extenuating clinical circumstances that prohibited the prescription of standard treatment. The two patients were both 22 years old on presentation. After the initial tumor resection, they both developed rapid deterioration in performance status within a few weeks due to leptomeningeal metastases. In view of the critical condition, BRAF and MEK inhibitors were prescribed as first line treatment. The two patients both achieved dramatic clinical response, which was parallel to the impressive radiological regression of the disease. Unfortunately, the duration of disease control was short as drug resistance developed rapidly. The two patients died 7 and 7.5 month after initial diagnosis of GBM. Primary treatment with inhibitors of BRAF and MEK can lead to tumor regression for patients with mutant glioblastoma. We therefore recommend that all young GBM patients should undergo BRAF mutation testing, especially for those with unusual aggressive clinical course.