The overall objective is to study the safety, pharmacokinetics and efficacy of linsitinib (a small molecule IGF-1R inhibitor) administered orally twice daily (BID) vs. placebo, at 24 weeks in the treatment of subjects with active, moderate to severe thyroid eye disease (TED).

Inclusion Criteria:

• Clinical diagnosis of Graves' Disease and/or autoimmune Hashimoto's thyroiditis associated with active moderate to severe TED with a CAS ≥ 4 (on the 7- item scale) for the most severely affected eye (primary study eye) at Screening and Baseline
• Confirmed active TED (not sight-threatening but has an appreciable impact on daily life, with onset (as determined by patient records) within 12 months prior to the Baseline visit and 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.
• Subjects must be euthyroid with the participant's baseline disease under control or have mild hypo- or hyperthyroidism (defined as free thyroxine [FT4] and free triiodothyronine levels [FT3] < 50% above or below the normal limits) at Screening.
• Does not require immediate ophthalmic surgery, radiotherapy to orbits or other ophthalmological intervention at the time of Screening and is not planning for any such treatment during the course of the study.

Exclusion Criteria:

• 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.
• Corneal decompensation unresponsive to medical management.
• Previous orbital irradiation or orbital surgery.
• Any glucocorticoid use (intravenous [IV] or oral) with a cumulative dose equivalent to >= 1g of methylprednisolone or equivalent for the treatment of TED within 3 months of Screening.
• Prior IGF-1R inhibitor therapy for any condition.

All individual participant data collected during the trial, after deidentification will be made available.

Beginning 3 months and ending 5 years following article publication.

Proposals should be directed to info@slingtx.com