RARE-54. MEK INHIBITION FOR AGGRESSIVE GLIOMAS IN ADULTS WITH NEUROFIBROMATOSIS TYPE 1

Abstract BACKGROUND Neurofibromatosis type 1 (NF1) is caused by mutations of the tumor suppressor gene NF1 resulting in decreased levels of neurofibromin and dysregulation of the RAS pathway, including MEK/ERK upregulation. Central nervous system malignancies have an overall standardized incidence ratio of 37.5 in population studies, with higher rates of aggressive gliomas in adults with NF1. Further, the response to standard glioma therapies in this population is mixed in published series. MEK1/2 inhibitors have shown activity in both NF1 driven plexiform neurofibromas and low grade gliomas, however, data is lacking about their optimal dose or sequencing relative to standard glioma therapies for adults with NF1 associated aggressive gliomas. We present recent experiences with the MEK1/2 inhibitor trametinib in adults with NF1 and newly diagnosed aggressive gliomas. METHODS A retrospective chart review was conducted on all adult patients with NF1 and astrocytoma treated with trametinib at the Johns Hopkins Brain Cancer Program from 2016 to 2018. RESULTS Four patients met selection criteria. Median age at diagnosis was 37 years [25–43]. Histologic diagnoses were: pilocytic astrocytoma (1), diffuse astrocytomas (2), and anaplastic astrocytoma (1). All tumors were IDH1 wild-type. Three received trametinib as frontline therapy (2 mg daily), one as second line treatment. All achieved a partial radiographic response within 2 months from the start of trametinib. Median overall survival was 15 months [4–19]; three patients are alive at publication, with a median of 12 months from diagnosis. Median progression-free survival was 2.5 months [1–11]. CONCLUSIONS Astrocytomas in adults with NF1, including histologically low-grade tumors, often have a more aggressive course than suggested by histology. These cases demonstrate clinical benefit from single agent MEK inhibition as well as possible synergistic effects with conventional therapies for gliomas in people with NF1, however, prospective investigation is needed.