Programmed Death-1 Inhibitor Immunotherapy-Induced Symptomatic Toxic Thyroid Nodule.

Immune checkpoint inhibitors, specifically programmed death-ligand 1 (PD-LI) inhibitors, are immune modifying medications that increasingly treat specific types of cancer. They are known to cause many side effects, including thyroid-related side effects. The use of PD-L1 inhibitors can cause hypothyroidism most commonly, while hyperthyroidism occurs less frequently. This case report describes a patient who developed a toxic thyroid nodule while taking the PD-L1 inhibitor, avelumab, for the treatment of Merkel cell carcinoma. It highlights the need for more research into the specific mechanisms by which these therapies can cause hyperthyroidism. It also raises the question regarding the association between the use of these medications and the development or worsening of thyroid nodules.