The overall objective is to investigate the efficacy, tolerability, and safety of teprotumumab (a fully human monoclonal antibody [mAb] inhibitor of the insulin-like growth factor-1 receptor [IGF-1R]) administered once every 3 weeks (q3W) for 21 weeks with a final assessment at Week 24, in comparison to placebo, in the treatment of participants with moderate-to-severe active thyroid eye disease (TED).

This is a randomized, double-masked, placebo-controlled, parallel-group, multicenter study. Approximately 76 participants (38/group) who meet the study eligibility criteria will be randomized on Day 1 in a 1:1 ratio (stratified by tobacco use status) to receive 8 infusions of teprotumumab or placebo q3W. All participants will enter a 24-week double-masked Treatment Period, during which study drug will be infused on Day 1 (Baseline), and Weeks 3, 6, 9, 12, 15, 18, and 21 (with a final visit at Week 24). All study drug dosing will be performed at the clinic under the supervision of clinic staff. On each dosing day, scheduled assessments (except for adverse event [AE] and concomitant medication use monitoring, which will be monitored throughout the clinic visit) will be completed prior to study drug dosing.

At the end of the double-masked Treatment Period (Week 24), participants who are proptosis non-responders (study eye has < 2 mm decrease in proptosis) will be eligible to enter an open-label extension study in which participants receive 8 infusions of teprotumumab in an open-label fashion.

At Week 24, proptosis responders, as well as non-responders who choose not to enroll in the open-label extension study, will enter a 48-week Follow-Up Period, during which study drug will not be administered and clinic visits are scheduled for Weeks 28, 36, 48, 60, and 72. Participants who are considered responders at Week 24 but who meet criteria for re-treatment due to relapse during the Follow-Up Period may enroll in the open-label extension study.

Participants who complete the Week 72 Visit will be contacted 6 and 12 months later via phone or email by research staff to enquire if any treatment for TED has been received since last study contact.

Study acquired from Horizon in 2024.

Inclusion Criteria:

1. Written informed consent.
2. Male or female participant between the ages of 18 and 80 years, inclusive, at Screening.
3. Clinical diagnosis of Graves' disease associated with active TED with a Clinical Activity Score (CAS) ≥ 4 (on the 7-item scale) for the most severely affected eye at Screening and Baseline.
4. Moderate-to-severe active TED (not sight-threatening but has an appreciable impact on daily life), usually associated with one or more of the following: lid retraction ≥ 2 mm, moderate or severe soft tissue involvement, exophthalmos ≥ 3 mm above normal for race and gender, and/or inconstant or constant diplopia.
5. Onset of active TED symptoms (as determined by participant records) within 9 months prior to Baseline.
6. Participants 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 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 clinical trial.
7. Does not require immediate surgical ophthalmological intervention and is not planning corrective surgery/irradiation during the course of the study.
8. Alanine aminotransferase (ALT) or AST ≤ 3 times the upper limit of normal (ULN) or serum creatine <1.5 times the ULN according to age at Screening.
9. Diabetic participants must have well-controlled stable disease (defined as HbA1C < 9.0% with no new diabetic medication [oral or insulin] or more than a 10% change in the dose of a currently prescribed diabetic medication within 60 days prior to Screening).
10. Women of childbearing potential (including those with an onset of menopause <2 years prior to Screening, non-therapy-induced amenorrhea for <12 months prior to Screening, or not surgically sterile [absence of ovaries and/or uterus]) must have a negative serum pregnancy test at Screening and negative urine pregnancy tests at all protocol-specified timepoints (i.e., prior to each dose and through Week 48 of the Follow-Up Period); participants who are sexually active with a non-vasectomized male partner must agree to use 2 reliable forms of contraception during the trial, one of which is recommended to be hormonal, such as an oral contraceptive. Hormonal contraception must be started at least one full cycle prior to Baseline and continue for 180 days after the last dose of study drug. Highly effective contraceptive methods (with a failure rate less than 1% per year) when used consistently and correctly, includes implants, injectables, combined oral contraceptives, intrauterine devices (IUDs), sexual abstinence or vasectomized partner.
11. Male participants must be surgically sterile or, if sexually active with a female partner of childbearing potential, must agree to use barrier contraceptive method from Screening through 180 days after the last dose of study drug.
12. Participant is willing and able to comply with the study protocol and evaluations for the duration of the study.

Exclusion Criteria:

1. Decreased best corrected visual acuity due to optic neuropathy as defined by a decrease in vision of 2 lines on the Snellen chart, new visual field defect, or color defect secondary to optic nerve involvement within the last 6 months.
2. Corneal decompensation unresponsive to medical management.
3. Decrease in CAS of ≥ 2 points in the study eye between Screening and Baseline.
4. Decrease in proptosis of ≥ 2 mm in the study eye between Screening and Baseline.
5. Previous orbital irradiation or surgery for TED.
6. Any steroid use (intravenous [IV] or oral) with a cumulative dose equivalent to ≥ 1 g of methylprednisolone for the treatment of TED. Previous steroid use (IV or oral) with a cumulative dose of <1 g methylprednisolone or equivalent for the treatment of TED and previous use of steroid eye drops is allowed if the corticosteroid was discontinued at least 4 weeks prior to Screening.
7. Corticosteroid use for conditions other than TED within 4 weeks prior to Screening (topical steroids for dermatological conditions and inhaled steroids are allowed).
8. Selenium and biotin must be discontinued 3 weeks prior to Screening and must not be restarted during the clinical trial; however, taking a multivitamin that includes selenium and/or biotin is allowed.
9. Any previous treatment with rituximab or tocilizumab. Use of any other non-steroid immunosuppressive agent within 3 months prior to Screening.
10. Use of an investigational agent for any condition within 60 days prior to Screening or anticipated use during the course of the trial.
11. Identified pre-existing ophthalmic disease that, in the judgment of the Investigator, would preclude study participation or complicate interpretation of study results.
12. Bleeding diathesis that in the judgment of the Investigator would preclude inclusion in the clinical trial.
13. Malignant condition in the past 12 months (except successfully treated basal/squamous cell carcinoma of the skin).
14. Pregnant or lactating women.
15. Current drug or alcohol abuse, or history of either within the previous 2 years, in the opinion of the Investigator or as reported by the participant.
16. Biopsy-proven or clinically suspected inflammatory bowel disease.
17. Known hypersensitivity to any of the components of teprotumumab or prior hypersensitivity reactions to mAbs.
18. Any other condition that, in the opinion of the Investigator, would preclude inclusion in the study.
19. Previous enrollment in this study or participation in a prior teprotumumab clinical trial.
20. Human immunodeficiency virus (HIV), hepatitis C or hepatitis B infections.

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.