• Age ≥ 18 years at the time of inclusion.

• Signed and dated written informed consent in accordance with ICH-GCP and local law prior to inclusion in the study.

• NF1 diagnosed (according to the international consensus criteria for evaluating NF1 \[18\]), see Appendix A.

• Confirmed PN by clinical assessment, USI, MRI, biopsy; one method is sufficient (histologic confirmation of PN is not necessary in the presence of radiographic findings).

• Existing of PN-associated symptoms.

• Adult patients (≥18 years) with newly diagnosed PN or established PN naïve to MEK-inhibitor therapy verified by medical records/histories (e.g., prior prescriptions, hospitalization data).