The overall objective is to evaluate the safety and efficacy of teprotumumab in the treatment of thyroid eye disease (TED) in participants who participated in the lead-in study HZNP-TEP-301 (NCT03298867; OPTIC) and who were either proptosis non-responders at Week 24 of HZNP-TEP-301 or were proptosis responders at Week 24 but met the criteria for re-treatment due to relapse during the Follow-Up Period of HZNP-TEP-301.

This is a multi-center, open-label extension study of HZNP-TEP-301 (NCT03298867) examining the safety and efficacy of teprotumumab in the treatment of TED in adult participants. Participants who complete the 24-week double-masked Treatment Period in Study HZNP-TEP-301 and are proptosis non-responders or are proptosis responders at Week 24 but meet the criteria for re-treatment due to relapse during the Follow-Up Period of HZNP-TEP-301 will be eligible for enrollment.

All participants who choose to participate will receive 8 infusions of teprotumumab (10 mg/kg for the first infusion followed by 20 mg/kg for the remaining 7 infusions) in an open-label fashion. The Baseline (Day 1) Visit of this extension study will occur within 14 days after the final visit of Study HZNP-TEP-301 (Week 24 for proptosis non-responders and up to Week 72 for participants who relapse). During the open-label Treatment Period, study drug infusions are scheduled for Day 1 (Baseline), and Weeks 3, 6, 9, 12, 15, 18, and 21, (with the final visit at Week 24). After completion of the Treatment Period, subjects who were proptosis non-responders in Study HZNP-TEP-301 will enter a 24-week Follow-Up Period during which study drug will not be administered and clinic visits are scheduled for 1, 3, and 6 months (Visits Month 7, 9, and 12) after the Week 24 visit. Subjects will be contacted 6 and 12 months later by phone or email to enquire if any treatment for TED had been received since the last study contact.

Participants who relapse during the Follow-Up Period of HZNP-TEP-301 and choose to enter this extension study will not participate in the Follow-Up Period of this study but will be contacted by phone or email 6 and 12 months after the Week 24 visit.

Study acquired from Horizon in 2024.

Inclusion Criteria:

• Written informed consent.
• Completed the 24-week double-masked Treatment Period in Study HZNP-TEP-301 (NCT03298867).
• Proptosis non-responder (< 2 mm reduction in proptosis in the study eye) at Week 24 of Study HZNP-TEP-301 OR proptosis responder at Week 24 who relapses during the Follow-Up Period of Study HZNP-TEP-301.
• Participant must be euthyroid with the baseline disease under control, or have mild hypo- or hyperthyroidism (defined as free thyroxine [FT4] and free triiodothyronine [FT3] levels < 50% above or below the normal limits) at the most recent clinic visit. Every effort should be made to correct the mild hypo- or hyperthyroidism promptly and to maintain the euthyroid state for the full duration of the clinical trial.
• Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤3 times the upper limit of normal (ULN) or serum creatinine <1.5 times the upper limit of normal (ULN; according to age) at the most recent clinic visit.
• Diabetic participants must have well-controlled disease (defined as hemoglobin A1C [HbA1c] < 9.0% at most recent clinic visit).
• Does not require immediate surgical ophthalmological intervention and is not planning corrective surgery/irradiation during the course of the study.
• Women of childbearing potential must have a negative urine pregnancy test at Baseline/Day 1. Participants who are sexually active with a non-vasectomized male partner must agree to use 2 reliable forms of contraception during the trial and continue for 180 days after the last dose of study drug. One of the 2 forms of contraception is recommended to be hormonal, such as an oral contraceptive. Hormonal contraception must be in use for at least one full cycle prior to Baseline. Highly effective contraceptive methods (with a failure rate less than 1% per year), when used consistently and correctly, includes implants, injectables, combined oral contraceptives, some intrauterine devices (IUDs), sexual abstinence or vasectomised partner.
• Male participants must be surgically sterile or, if sexually active with a female partner of childbearing potential, must agree to use a barrier contraceptive method from Baseline through 180 days after the last dose of study drug.
• Participant is willing and able to comply with the prescribed treatment protocol and evaluations for the duration of the study.
• Has not received any treatment for TED since Week 24 of the of the HZNP-TEP-301 study.

Exclusion Criteria:

• Participants will be ineligible if, in the opinion of the Investigator, they are unlikely to comply with the study protocol or have a concomitant disease or condition that could interfere with the conduct of the study or potentially put the participant at unacceptable risk.
• The exclusion criteria (except those related to screening) of protocol HZNP-TEP-301(NCT03298867) also apply to this open-label extension study.

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.