This study investigates the use of an investigational medication for patients with neurofibromatosis type 1 (NF1), a genetic disorder that causes tumors to form on nerve tissue. The study focuses on patients with inoperable, progressive, or symptomatic plexiform neurofibromas (PN), which are complex tumors associated with NF1. These patients have no alternative therapeutic options available.

Participants will receive the investigational medication in an open-label, single-arm setting, meaning all participants will receive the same treatment without a placebo. The study is designed to provide access to this medication as long as patients continue to benefit from it. Approximately 100 patients in the US will be involved.

• Who can participate: Patients aged 2 and older with neurofibromatosis type 1 (NF1) who have exhausted all approved therapies can participate. Participants must be able to swallow whole capsules and have normal cardiac function and adequate blood pressure.
• Study details: Participants will take the investigational medication in capsule form. The study is open-label, meaning all participants receive the medication, and there is no placebo group.