An Extensive-stage Small-cell Lung Cancer Case With Preexisting Lambert-Eaton Myasthenic Syndrome Successfully Treated With an Immune Checkpoint Inhibitor

• Immune checkpoint inhibitor (ICI) therapy could exacerbate preexisting active autoimmune diseases (AIDs), and the presence of preexisting AIDs might be associated with a greater risk of developing new immune-related adverse events (irAEs). • The safety of ICIs for patients with Lambert-Eaton myasthenic syndrome (LEMS), a neuromuscular autoimmune disease known as a paraneoplastic syndrome mainly associated with small-cell lung cancer (SCLC), is fully unknown. • We experienced an extensive-stage (ES)-SCLC patient with LEMS successfully treated with chemotherapy in combination with ICI without a flare-up of LEMS. • Phase III trials have shown that ICIs in combination with platinum doublet therapy significantly improved the overall survival of patients with ES-SCLC in first-line settings, therefore, patients diagnosed with ES-SCLC with the complication of LEMS have the widespread opportunity to receive ICIs as standard care. This report suggests that treatment using ICIs may be a treatment option to consider for ES-SCLC patients with LEMS. © 2021 The Authors