A Study to Investigate Efficacy and Safety of TOUR006 in Participants 18 to 80 Years of Age With Thyroid Eye Disease

Phase 2b trial of TOUR006 in Thyroid Eye Disease (TED) to evaluate 20mg and 50mg doses against placebo given by a subcutaneous injection every eight weeks to TED patients who are in the active inflammatory phase of disease.

Inclusion Criteria: * Clinical diagnosis of Graves' disease associated with moderate to severe active TED * Onset of active TED symptoms within approximately 15 months * Proptosis (exophthalmos) ≥3 mm above the normal range per investigator judgment (based upon race and gender) for the study eye * CAS ≥4 (on the 7-item scale) for the study eye * Presence of TSI \>130% of the normal reference standard or \>0.55 IU/L (depending on assay method) and laboratory reference ranges Additional inclusion criteria are defined in the study protocol. Exclusion Criteria: * Anticipated need for intervention due to sight-threatening complications or other significant and acute deterioration in vision * Any previous treatment with teprotumumab or other agent that inhibits the IGF-1 receptor * History of systemic (eg, oral or IV) steroid use with a cumulative dose equivalent to \>1 g of methylprednisolone for the treatment of TED. Previous oral steroid use with a cumulative dose of ≤1g methylprednisolone (or equivalent dosage for other systemic corticosteroid) for the treatment of TED, however, is allowed if the corticosteroid was discontinued at least 6 weeks before baseline (Day 1) and completely tapered by Baseline (if applicable). * Systemic (oral or IV) corticosteroid use for conditions other than TED within 6 weeks of baseline (Day 1) or not completely tapered by baseline (if applicable). * Any major illness/condition or evidence of an unstable clinical condition that, in the investigator's judgment, will substantially increase the risk to the participant, or confound the interpretation of safety assessments, if they were to participate in the study * Any other condition that, in the opinion of the investigator, would impair the ability of the participant to comply with the study procedures or impair the ability to interpret data from the participant's participation in the study * Pregnant or lactating Additional exclusion criteria are defined in the study protocol.