**4.1 Thyroid dysfunction**

Thyroid dysfunction is one of the most common AEs observed during PD-1 inhibition and is heterogeneous in nature. In a study of 73 patients who underwent nivolumab therapy, Peiro et al. [163] reported that 23.3% of patients developed thyroid dysfunction. Among them, seven patients showed thyrotoxicosis and 10 patients showed primary hypothyroidism (four required levothyroxine treatment). They concluded that thyrotoxicosis occurred earlier than hypothyroidism. Before the onset of hypothyroidism, 33% of patients exhibited transient thyroiditis and five patients had hyperthyroid, which became hypothyroid later. In cases of thyroiditis, patients can be treated with beta-blockers, and thyroid hormone replacement may be required for hypothyroidism. For hyperthyroidism, beta-blockers and corticosteroids are very effective [164].
