A previous study reported that treatment with anti-PD-1 antibodies can cause a flare-up of a pre-existing autoimmune disease.28 In that study, flare-ups occurred in 14/27 (52%) patients with rheumatologic disorders, 3/8 with psoriasis, 2/2 with immune thrombocytopenic purpura and 1/4 with Graves’ disease.28 However, it was unclear if hyperthyroidism or destructive thyroiditis was involved in the pathogenesis of thyrotoxicosis in the patient with a Graves’ disease flare-up. Here, PDCD1 is linked to psoriasis.