Following treatment with an PD-1 inhibitor for malignant melanoma, the patient developed refractory hypokalemia that was unresponsive to potassium chloride infusion and oral supplementation, graded as CTCAE 5.0 Grade 3, accompanied by CTCAE 5.0 Grade 2 fatigue and no other discomfort, tests of the Reproductive Hormone Panel, thyroid function, cortisol rhythm, and ACTH rhythm ruled out hypophysitis. This evidence concerns the gene POMC and melanoma.