Sponsor decision.

The purpose of this study is to understand treatment patterns and assess long-term effectiveness and safety outcomes associated with selumetinib treatment as well as to explore clinical and non-clinical factors affecting those outcomes in patients with neurofibromatosis type 1 (NF1) and plexiform neurofibromas (PNs) who started selumetinib between the ages of 2 to 18 years inclusive, and initiated selumetinib treatment on or after 10 April 2020 in a real-world setting.

This is a US observational registry of pediatric NF1 PN participants treated with selumetinib.

Inclusion Criteria:

• Participants diagnosed with NF1 and PN
• Started selumetinib between the ages of 2 to 18 years inclusive, and initiated selumetinib treatment on or after 10 April 2020, including patients who:
• Discontinued selumetinib before enrollment; or
• Initiated treatment before enrollment and are currently on selumetinib; or
• Initiated selumetinib on the day of enrollment or intend to initiate selumetinib within 3 months after enrollment
• Able to give written informed consent. Participant or participant's parent/legal guardian must be willing and able to give written informed consent and the participant (if minor) must be willing to give written informed assent.

Exclusion Criteria:

• Participants currently participating in any clinical trials at time of enrollment or initiation of selumetinib.

Approximately 200 participants who meet the eligibility criteria will be enrolled from 20-25 sites.

Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.