[A Case of Isolated ACTH Deficiency Induced by Nivolumab in a Patient with Gastric Cancer Metastasis of the Peritoneum].

Nivolumab induces several immune-related adverse events. Isolated adrenocorticotropic hormone(ACTH)deficiency has low frequency. A 73-year-old woman with gastric cancer metastasis of the peritoneum was treated with nivolumab as the third-line chemotherapy. After 5 courses of nivolumab, she developed hypothyroidism. After completing 12 courses, peritoneal metastasis increased. We evaluated the metastasis as progression of disease, so treatment with nivolumab was discontinued. Two weeks after the last dosage of nivolumab, she developed general fatigue and appetite loss. At first, we considered that these symptoms were caused by peritoneal metastasis, but progression was not indicated in the CT. Blood levels of cortisol and ACTH were very low. We suspected secondary adrenocortical insufficiency induced by nivolumab. Endocrinological examinations and the results of brain MRIsuggested isolated ACTH deficiency. This is the first report of isolated ACTH deficiency induced by nivolumab in a patient with gastric cancer metastasis of the peritoneum. The symptoms of adrenocortical insufficiency induced by nivolumab overlap with those of peritoneal metastasis, and thus, it may be difficult to confirm a differential diagnosis. When adrenocortical insufficiency is suspected, we should check the blood levels of cortisol and ACTH.