A Case of Lung Adenocarcinoma with Long-Term Response after Late-Onset Pembrolizumab-Induced Acute Adrenal Insufficiency

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.