Pembrolizumab is an anti-programmed cell death protein-1 antibody that is mainly used for the treatment of non-small cell lung cancer (NSCLC). Immune-related adverse events can be caused by immune checkpoint inhibitors; however, few case reports evaluate the prognosis of patients with NSCLC with late-onset immune-related adverse events. In this case, a 63-year-old man with stage IVA lung adenocarcinoma received pembrolizumab as first-line therapy and achieved a complete response. The patient developed hypothyroidism and skin toxicity owing to pembrolizumab over the course of treatment; however, the patient continued with pembrolizumab. The patient discontinued pembrolizumab after 20 cycles owing to appetite loss from 14 months after the initiation of pembrolizumab. Two months later, the symptoms worsened and the patient was taken to hospital by an ambulance owing to movement difficulty. The patient was diagnosed with acute adrenal insufficiency by endocrinological examinations. The condition of the patient improved after hydrocortisone treatment. Sixteen months have passed without the readministration of pembrolizumab and no recurrence of lung adenocarcinoma has been observed. Late-onset, severe, and diverse immune-related adverse events may be a favorable prognostic factor associated with survival.

We herein report a rare case of advanced lung adenocarcinoma with central diabetes insipidus due to pituitary metastasis. Although treatment with gefitinib was dramatically effective, the symptoms of diabetes insipidus did not improve. Radiotherapy for pituitary metastasis was effective to control diabetes insipidus; however, we could not cease the administration of 1-deamino-8-arginine vasopressin (DDAVP). It is important for physicians to positively consider radiotherapy for pituitary metastases even if favorable tumor control is achieved with chemotherapy when diabetes insipidus becomes clinically overt. Furthermore, continuous DDAVP administration may be needed to treat central diabetes insipidus.