The study consists of a randomized double-masked, placebo-controlled, parallel-group, multicenter trial with an optional open-label treatment period for proptosis non-responders who complete the Double-masked Treatment Period.

The main objective of the study is to evaluate the effect of teprotumumab subcutaneous administration versus placebo on the proptosis responder rate (ie, the percentage of participants with a ≥ 2-mm reduction from Baseline in the study eye without deterioration [≥ 2-mm increase] of proptosis in the fellow eye) at Week 24.

Acquired from Horizon in 2024.

Inclusion Criteria:

1. Participant must provide written informed consent.
2. Participant can be male or female and must be between the ages of 18 and 80 years, inclusive, at Screening.
3. Participant must have a clinical diagnosis of Graves' disease associated with active TED with a CAS ≥ 3 (on the 7-item scale) for the most severely affected eye at Screening and Baseline.
4. Participant must have moderate-to-severe active TED (not sight-threatening but has an appreciable impact on daily life), usually associated with 1 or more of the following: lid retraction ≥ 2 mm, moderate or severe soft tissue involvement and/or inconstant or constant diplopia. (Note: Participants with no diplopia at Baseline will be limited to approximately 25% of the total number enrolled.)
5. Participant has proptosis ≥ 3 mm from Baseline (prior to diagnosis of TED), as estimated by treating physician, and/or proptosis ≥ 3 mm above normal for race and gender.
6. Participant had onset of active TED symptoms (as determined by participant records) within 15 months prior to Baseline.
7. Participants must be euthyroid with the baseline disease under control or have mild hypoor hyperthyroidism (defined as free thyroxine [FT4] and free triiodothyronine [FT3] levels < 50% above or below the normal limits) at Screening. 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 trial.
8. Participant does not require immediate surgical ophthalmological intervention and is not planning corrective surgery/irradiation during the trial.
9. Women of childbearing potential must have a negative serum pregnancy test at Screening and negative urine pregnancy tests at all protocol-specified time points (ie, prior to each dose and throughout participation in the trial).
10. Participant is willing and able to comply with the protocol requirements for the duration of the trial.

Exclusion Criteria:

1. Participant has decreased best-corrected visual acuity due to optic neuropathy, defined by a decrease in vision of 2 lines on the Snellen chart (or equivalent), new visual field defect or color defect secondary to optic nerve involvement within the last 6 months.
2. Participant has corneal decompensation unresponsive to medical management.
3. Participant has a decrease in CAS of ≥ 2 points between Screening and Baseline.
4. Participant has a decrease in proptosis of ≥ 2 mm between Screening and Baseline.
5. Participant had prior orbital irradiation, orbital decompression or strabismus surgery (excluding childhood strabismus surgeries unrelated to TED/Graves' disease).
6. Participant is planning to have eyelid surgery during the trial.
7. Participant received periocular botulinum toxin injection within 12 months prior to Screening.
8. Participant has any systemic use of a steroid (IV or oral) or steroid eye drops for the treatment of TED or other conditions within 3 weeks prior to Screening. Exceptions include local administration (excluding periocular), eg, topical, intra-articular, and inhaled steroids, as well as steroids used to treat infusion reactions.

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.