Case Reports of Teprotumumab as Treatment for Monoclonal Antibody-Induced Thyroid Orbitopathy.

: Targeted biologic therapies, especially monoclonal antibodies (mAbs) such as nivolumab and alemtuzumab, have revolutionized treatment for malignancies and autoimmune conditions but can cause rare immune-related adverse events (IRAEs), including orbitopathy. To date, only a handful of cases have described the treatment of thyroid eye disease secondary to mAbs, and even fewer have described how to treat refractory disease. : We are illustrating two cases in this report: a 73-year-old woman who developed thyroid eye disease (TED) after nivolumab therapy for melanoma, and a 36-year-old man who presented with TED following alemtuzumab treatment for multiple sclerosis. Both patients failed corticosteroid therapy but showed a significant improvement with teprotumumab, an anti-insulin-like growth factor (IGF)-1 receptor mAb. : These cases highlight underrecognized orbital IRAEs linked to mAb therapy and demonstrate teprotumumab's potential as an effective option for steroid-refractory thyroid orbitopathy. Clinicians should maintain an awareness of orbital complications in patients receiving mAbs to enable prompt diagnosis and intervention, minimizing visual morbidity. Further studies are needed to clarify the pathogenesis of mAb-associated orbitopathy and to establish evidence-based treatment protocols for these rare but impactful complications.