Immune checkpoint inhibitor-related thyroid dysfunction

Immune-related adverse events (irAEs) are caused by immune checkpoint inhibitors in several organs including the endocrine glands. Thyroid dysfunction (thyroid irAEs) is often observed among endocrine irAEs and is induced by blockade of programmed cell death 1 (PD-1), programmed death ligand 1, or PD-1 plus cytotoxic T-lymphocyte antigen 4. Endocrinologically, destructive thyroiditis or hypothyroidism is observed in most cases, whereas hyperthyroidism (Graves' disease) is rare. Most patients who develop destructive thyroiditis or hypothyroidism subsequently require thyroid hormone replacement therapy. Thyroid irAE development is associated with prolonged survival in patients with non-small cell lung carcinoma. The incidence of thyroid irAEs is higher in patients who are positive versus negative for anti-thyroid antibodies at baseline, suggesting that these antibodies can predict thyroid irAE development. Cytotoxic T cells, especially CD4 T cells, are reportedly involved in the development of destructive thyroiditis. In this review, we describe the clinical features, potential biomarkers, and mechanism of thyroid irAEs.