Serological aggravation of autoimmune thyroid disease in two cases receiving nivolumab

Nivolumab, a blockade of programmed cell death 1, is now administrated for advanced malignant melanomas. Nivolumab‐associated adverse events include organ‐specific autoimmune disorders; autoimmune thyroid disease, vitiligo and insulin‐dependent diabetes. However, predisposed persons are currently unknown. Here, we report serological aggravation of autoimmune thyroid disease in two cases receiving nivolumab: one with Hashimoto disease and another with probable subclinical Hashimoto disease. We should verify if nivolumab‐related hypothyroidism and hyperthyroidism are predisposed to occur in euthyroid individuals with subclinical autoimmune thyroid disease.