A Phase I/II, Single-Arm, Open Label Study to Evaluate the Pharmacokinetics, Safety/Tolerability and Efficacy of the Selumetinib Granule Formulation in Children Aged ≥1 to <7 Years With Neurofibromatosis Type 1 (NF1) Related Symptomatic, Inoperable Plexiform Neurofibromas (PN) (SPRINKLE)

This study consists of a screening period (up to 28 days), a treatment period (25 cycles) and a long term safety follow-up for participants until they are 5 years old or commence an alternative systemic NF1-PN treatment, whichever is the earlier. Participants may continue treatment with selumetinib throughout the long term safety follow-up as long as they are considered to be receiving clinical benefit in the opinion of their Investigator. A safety follow up assessment will be performed 30 days after the last dose of study intervention for all study participants.

Selumetinib granule formulation will be administered using BSA-based dosing. The granule formulation dose schema to be used in the study will be established in the dose finding phase. At enrolment participants must have a BSA within the range 0.40 to 1.09 m2; once participants attain a BSA between 1.10 and 1.29 m2 they will be encouraged to transition to the capsule formulation, if feasible, although all participants must remain on the granule formulation until after they have completed their third cycle of treatment.

Selumetinib capsule formulation will be administered using BSA-based dosing. Once participants attain a BSA between 1.10 and 1.29 m2 they will be encouraged to transition to the capsule formulation, if feasible, although all participants must remain on the granule formulation until after they have completed their third cycle of treatment.