<h4>Objective</h4>To evaluate a case of pembrolizumab-induced hypoparathyroidism leading to hypocalcemia.<h4>Methods</h4>The diagnostic tests performed included calcium and parathyroid hormone level detection and calcium-sensing receptor gene analysis.<h4>Results</h4>A 71-year-old Caucasian man was diagnosed with stage IIIB adenocarcinoma of the lung and received radiation therapy but had no other exposure to radiation. The gene discussed is CASR; the disease is Hypocalcemia.