Suzuki K, Terakawa T, Furukawa J, et al. - Researchers retrospectively gathered data for 5 (10.2%) patients who developed adrenal insufficiency after treatment with nivolumab for metastatic renal cell carcinoma (mRCC) or unresectable renal cell carcinoma at Kobe University Hospital between December 2016 and August 2018, to unveil the clinical characteristics of adrenal insufficiency associated with nivolumab in patients with mRCC. The included cases had secondary adrenal insufficiency because of isolated hyposecretion of adrenocorticotropic hormone. Four patients had eosinophilia at the onset of symptoms. Brain magnetic resonance imaging-detected signs of hypophysitis were not identified in any of the cases. All cases had normal secretion of other pituitary hormones. Hydrocortisone replacement therapy at a physiological dose resulted in the improvement of the conditions of all patients. A partial response to nivolumab was demonstrated by all 5 patients and these patients continued to be stable following the suspension of nivolumab. A case series of adrenal insufficiency caused by nivolumab in patients with mRCC has been detailed for the first time in this study. The likelihood that adrenal insufficiency may be related to a favorable response to nivolumab in patients with mRCC was also suggested.