Background: The neurofibromin 1 (NF1) protein regulates the downstream RAS/RAF/MEK/ERK pathway and functions as a tumor suppressor. Somatic pathogenic mutations in NF1 are found in approximately 4.7%-10% of NSCLC, with a higher frequency in lung adenocarcinomas, reaching up to 15% in certain cohorts. Trametinib, a MEK inhibitor, has demonstrated activity in tumors with NF1 alteration in preclinical models, and clinical activity in low-grade glioma and plexiform neurofibromas in neurofibromatosis type 1. Trametinib had only limited clinical efficacy in other tumor types with NF1 mutations in the NCI-Match trial. However, the sole NSCLC patient that was evaluable for response in the NCI-Match trial benefited from a deep partial response. More data for the activity of MEK inhibitors in NF1 altered NSCLC are needed.

Cases presentation: We report here a series of four NSCLC patients with NF1 pathogenic mutations treated with trametinib. All patients underwent extensive molecular testing with next-generation sequencing (custom 462-gene panel) and copy number variation analysis and were deemed to have potential NF1 -loss-driven tumors after a case discussion in a multidisciplinary molecular tumor board. Two patients exhibited homozygous NF1 LOF alterations, whereas two patients had heterozygous loss-of-function alterations. All patients were treated with oral trametinib 2 mg once daily, after failure of standard therapies. Trametinib was administered for a maximum duration of 9 weeks. The best response observed was a stable disease in one patient. All patients died within 3 months of treatment initiation. No side effects warranted treatment cessation.

Conclusion: In this small case series, NSCLC patients with NF1 alterations did not derive clinical benefit from trametinib. While these data do not support trametinib as a treatment option for NF1 -mutated NSCLC, larger studies are required to draw firm conclusions.