Nivolumab-induced hypophysitis in a patient with advanced malignant melanoma

The anti-programmed cell death-1 monoclonal antibody (mab), nivolumab has recently been approved for the treatment of unresectable or metastatic malignant melanoma and non-small-cell lung cancers in Japan. Ipilimumab, an anti-cytotoxic T lymphocyte antigen-4 mab for malignant melanoma that was approved earlier than nivolumab in Western countries, is known to frequently cause endocrine immune-related adverse events such as hypophysitis and thyroid dysfunction. We herein report a patient with advanced melanoma who appeared to develop hypophysitis as a consequence of the inhibition of PD-1 by nivolumab. One week after the 6^th administration of nivolumab, the patient developed progressive fatigue and appetite loss. Laboratory data on admission for the 7^th administration of nivolumab showed eosinophilia and hyponatremia. Since ACTH and cortisol levels were low, nivolumab was discontinued and a large dose of hydrocortisone (100 mg/d) was promptly administered intravenously. A magnetic resonance imaging scan revealed the mild enlargement of the anterior pituitary gland and thickening of the stalk with homogenous contrast. A detailed assessment of anterior pituitary functions with hypothalamic hormone challenges showed that hormonal secretions other than ACTH and TSH were normal. With a replacement dose of hydrocortisone (20 mg/d), the 7^th administration of nivolumab was completed without exacerbating the patient's general condition. The present report provides the first detailed endocrinological presentation of nivolumab-induced hypophysitis showing the enlargement of the pituitary gland and stalk in a malignant melanoma patient in Japan. Oncologists and endocrinologists need to be familiar with potentially life-threatening hypophysitis induced by immune-checkpoint inhibitors.