A Study of TEPEZZA® Treatment in Participants With Thyroid Eye Disease

Inclusion Criteria: 1. Thyroid eye disease (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, proptosis, and/or inconstant or constant diplopia. 2. Proptosis ≥ 3 mm increase from the participant's baseline (prior to diagnosis of TED), as estimated by treating physician and/or proptosis ≥ 3 mm above normal for race and gender. 3. Participant must be euthyroid with baseline disease under control or have mild hypo- or hyperthyroidism 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. 4. Does not require immediate surgical ophthalmological intervention. 5. Participants with diabetes must have HbA1c ≤ 8.0% at Screening. Exclusion Criteria: 1. Decreased best-corrected visual acuity due to optic neuropathy within the last 6 months. 2. Corneal decompensation unresponsive to medical management in the study eye. 3. Decrease in proptosis of ≥ 2 mm in the study eye between Screening and Baseline. 4. Alanine aminotransferase or aspartate aminotransferase \> 3x the upper limit of normal or estimated glomerular filtration rate ≤ 30 mL/min/1.73 m2 at Screening. 5. Use of any steroid (IV, oral, steroid eye drops) for the treatment of TED or other conditions within 3 weeks prior to Screening. Steroids cannot be initiated during the trial. Exceptions include topical and inhaled steroids and steroids used to treat infusion reactions. 6. Any treatment with rituximab, tocilizumab, or any other non-steroid immunosuppressive agent within 90 days prior to the first injection of investigational product on Day 1. 7. Any previous treatment with HZN-001 or TEPEZZA (teprotumumab-trbw), including previous enrollment in this trial or participation in a prior TEPEZZA trial. 8. Treatment with any mAb within 3 months prior to Screening.