A Study to Assess the Long-term Safety and Efficacy of Erenumab (AMG 334) in Chronic Migraine Prevention.

This was a multicenter, 52-week, open-label study designed to assess the long-term safety and
efficacy of erenumab in adults with chronic migraine. Participants who completed the 12-week
double-blind treatment of the parent Study 20120295 (NCT02066415) and met all Study 20130255
eligibility criteria were eligible for enrollment into this study. Enrollment occurred within
14 days after the parent study's week 12 visit.

The initial dose used in the study was erenumab 70 mg every month (QM). The protocol was
subsequently amended to increase the dose to erenumab 140 mg QM (Protocol Amendment 2).
Participants who had already completed the week 28 visit (ie, midpoint of the study) at the
time of Protocol Amendment 2 continued to receive open-label erenumab 70 mg QM for the
remainder of the study. Participants who enrolled but had not completed the week 28 visit at
the time of Protocol Amendment 2 increased the open-label erenumab dose from 70 mg QM to 140
mg QM at the next visit. All participants who enrolled after Protocol Amendment 2 received
open-label erenumab 140 mg QM throughout the study.

Participants may elect to participate in a separate clinical home use (CHU) substudy to
assess subjects' ability to self-administer 140 mg of erenumab for in-home use using either
two prefilled syringes (PFS) or two prefilled autoinjector/pens (AI/pens). Enrollment in the
12-week substudy occurred at either week 12 or week 40 of study 20130255. Participants were
randomized to self-administer erenumab using either the PFS or AI/pen on CHU days 29 and 57
at home.

Inclusion Criteria:

1. Subject has provided informed consent prior to initiation of any study-specific
activities/procedures

2. Completed the 12-week study visit and did not end IP early during the double-blind
treatment period of the AMG 334 20120295 (NCT02066415) parent study, and is
appropriate for continued treatment.

Exclusion Criteria:

1. Development of any unstable or clinically significant medical condition, laboratory or
electrocardiogram (ECG) abnormality following randomization into the parent study,
that in the opinion of the investigator, would pose a risk to subject safety or
interfere with the study evaluation, procedures or completion.

2. Systolic blood pressure (BP) 160 mm Hg and/or diastolic BP 100 mm Hg or greater at
screening/Day 1.

3. Subject who used excluded concomitant medications between week 8 and week 12 of the
parent study