小細胞肺癌 (small cell lung cancer, SCLC) 是侵襲性強且致命的癌症，可分為侷限期 (limited-stage) 與擴散期 (extensive-stage) SCLC，前者可治癒，應接受以根除為目標的治療方式，例如：手術治療或同步化學放射治療。擴散期 SCLC 在過去 30 年其治療幾無進展，多依賴全身性化學治療與放射治療。近年來，癌症免疫治療 (cancer immunotherapy) 進展快速，其中免疫檢查點抑制劑 (immune checkpoint inhibitors, ICIs) 已有多個藥物核准上市。ICIs 中抑制 PD-L1 (programmed cell death protein ligand 1) 之單株抗體 atezolizumab 或 durvalumab 合併標準化學治療，已取得美國食品藥物管理局 (U.S. Food and Drug Administration, FDA) 和行政院衛生福利部食品藥物管理署 (Taiwan Food and Drug Administration, TFDA) 核准用於第一線治療擴散期 SCLC，能明顯延長無惡化存活期 (progression-free survival) 以及整體存活期(overall survival)，這個組合儼然已成為擴散期 SCLC 的第一線標準治療。抑制 PD-1 (programmed cell death protein 1) 之單株抗體 pembrolizumab 目前則暫時取得 FDA 和TFDA 核准用於治療先前至少已接受兩種治療的局部晚期或轉移性 SCLC 病人。然而，此適應症係屬加速核准，仍待確認性試驗以證明其臨床效益。使用 ICIs 發生不良事件的比例比傳統化學治療低，但少數病人仍會發生嚴重免疫相關不良事件 (immunerelated adverse events)，因此需要醫療人員及早發現並處理之。

Small cell lung cancer (SCLC), an aggressive and devastating malignancy, is characterized by rapid growth and early metastasis. Early concurrent chemoradiation is the standard care for limited-stage SCLC. Platinum-based chemotherapy in the United States and Europe and irinotecan plus platinum in Japan have remained the mainstay of first-line treatment for extensive-stage SCLC. Although most patients respond to first-line chemotherapy, the majority of patients rapidly relapse. Fortunately, immunotherapy, mainly including immune checkpoint inhibitors (ICIs) that target the cytotoxic T lymphocyte antigen-4 (CTLA-4), checkpoints programmed death protein 1 (PD-1), and programmed death protein ligand 1 (PD-L1) to block immune regulatory checkpoints on tumor cells, and immune cells, has made progress in the treatment of SCLC in recent years. The combination of immunotherapy, such as atezolizumab or durvalumab, with chemotherapy has significantly improved overall survival and progression-free survival in patients with limited-stage SCLC and become first-line treatment. Most SCLC initially respond to first line therapy but almost invariably recur. Topotecan and amrubicin (in Japan) remain the primary chemotherapy options for relapsed SCLC. U.S. and Taiwan Food and Drug Administration granted accelerated approval to pembrolizumab for the treatment of patients with metastatic SCLC with disease progression on or after platinumbased chemotherapy and at least 1 other prior line of therapy. Confirmatory trials are still pending to prove its clinical benefits. While ICIs are characteristic of less adverse effects compared with chemotherapy, health-care providers should be aware of and ready for immune-related adverse events, including colitis, hepatitis, endocrine diseases, and pneumonitis.