Use of Immunotherapy in Extensive-Stage Small Cell Lung Cancer

Lung cancer is a leading cause of cancer death in the United States and around the world. Approximately 13% of lung cancers are small cell lung cancer (SCLC). SCLC is generally classified as a limited-stage and extensive-stage disease depending on the extent of involvement. For patients with the extensive-stage disease, until recently, chemotherapy alone has been the recommended treatment, although radiotherapy could be used in select patients for palliation of symptoms. The standard of care for extensive-stage SCLC is platinum doublet chemotherapy with either cisplatin or carboplatin in combination with etoposide. Even though first-line therapy has an initial response rate of 60-80%, the prognosis is poor, with overall survival of 10-12 months. The only FDA-approved second line of therapy is topotecan, approved both as an intravenous formulation as well as an oral formulation, with response rates of 6-12% in chemorefractory disease and 15-37% in chemosensitive disease. Immunotherapy has recently been approved as a first-line agent in metastatic SCLC in combination with chemotherapy. It is also approved as a third-line agent in metastatic SCLC after the failure of two chemotherapy regimens. The FDA approved four drugs, two of them being PD-1 inhibitors (pembrolizumab, nivolumab), and two of them being PD-L1 inhibitors (atezolizumab and durvalumab) in SCLC. This review article summarizes the significance of immunotherapy in the treatment of extensive-stage SCLC, its side effects, and limitations.