Background: While the use of immunotherapy has revolutionised the treatment of various cancers, it is often associated with a myriad of immune-related adverse effects.
Case Presentation: In this article, we report a rare case of durvalumab-induced triple-M syndrome in a 69-year-old woman with stage III lung adenocarcinoma. She was admitted with profound generalised muscle weakness, myalgia, and exertional breathlessness, about a week into her second cycle of durvalumab, an immune checkpoint inhibitor.