This study will evaluate the efficacy and safety of erenumab in migraine prevention in children (6 to <12 years) and adolescents (12 to <18 years) with chronic migraine. The study hypothesis is that in pediatric participants with chronic migraine, the combined erenumab dose group has a greater reduction from baseline to week 9 through week 12 (month 3) in monthly migraine days (MMDs) when compared with placebo in the double-blind treatment phase (DBTP).

This study is a phase 3, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the efficacy and safety of erenumab in migraine prevention in children (6 to <12 years) and adolescents (12 to <18 years) with chronic migraine. The trial consists of four phases: screening (up to 3 weeks of initial screening and a 4-week prospective baseline phase); the DBTP (24 weeks for Group 1 subjects; 12-weeks for Group 2 subjects) in which participants receive placebo or erenumab dose 1, dose 2 or dose 3 (based on participant's body-weight) via subcutaneous injection once a month; the optional dose level blinded extension phase (40 weeks), in which all participants are assigned to receive dose 1, dose 2 or dose 3 of erenumab; and a 12 weeks safety follow-up phase (16 weeks after the last dose of investigational drug). The study intends to enrol 286 participants (256 adolescents and 30 children).

Inclusion Criteria:

• Children (6 to less than 12 years of age) or adolescent (12 to less than 18 years of age) at the time of signing, if developmentally appropriate, the formal assent to participate to the study.
• Participant's parent or legal representative has provided written informed consent before initiation of any study-specific activities/procedures.
• History of migraine (with or without aura) for ≥ 12 months before screening according to the IHS Classification ICHD-3 (Headache Classification Committee of the International Headache Society, 2013) ICHD-3 specifications for pediatric migraine (participants aged less than 18 years), should be considered for the diagnosis of migraine.
• History of ≥ 15 headache days per month of which ≥ 8 headache days were assessed by the participant as migraine days per month in each of the 3 months prior to screening.
• Migraine frequency: greater than or equal to 8 migraine days based on the eDiary data during the last 28 days of the baseline phase if more than 28 days in duration.
• Headache frequency of greater than or equal to 15 headache days based on the eDiary data during the last 28 days of the baseline phase if more than 28 days in duration.
• Demonstrated at least 80% compliance with the eDiary based on the last 28 days of the baseline period, if more than 28 days in duration (eg, completing eDiary items for at least 23 out of the last 28 days of the baseline phase).

Key Exclusion Criteria:

• History of cluster headache or hemiplegic migraine headache.
• Chronic migraine with continuous pain, in which the participant does not have any pain free periods (of any duration) during the 1 month prior to screening.
• No therapeutic response with greater than 3 medication categories for prophylactic treatment of migraine after an adequate therapeutic trial. No therapeutic response is defined as no reduction in headache frequency, duration, or severity after administration of the medication for at least 6 weeks at the generally-accepted therapeutic dose(s) based on the investigator's assessment.
• History of suicidal behavior or the participant is at risk of self-harm or harm to others.
• History of major psychiatric disorder. Participants with anxiety disorder and/or mild major depressive disorder (Patient Health Questionnaire Modified for Adolescents [PHQ-A] score 9 for adolescents or based on medical judgement of the investigator for children) are permitted in the study if they are considered by the investigator to be stable and are taking no more than 1 medication for each disorder. Participants must have been on a stable dose within the 3 months before the start of the baseline phase.

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.