The role of immunotherapy in small cell lung cancer

Despite decades of research, prognosis for SCLC patients remains poor, and treatment options limited. SCLC is an immunogenic tumor with high somatic mutation rates due to tobacco exposure resulting in potential neo-antigens, the presence of suppressed immune responses, and occurrence of paraneoplastic disorders. The use of T cell immune-checkpoint inhibitors (anti-PD1: nivolumab, pembrolizumab; anti-PD-L1: atezolizumab, durvalumab; anti-CTLA-4: ipilimumab, tremelimumab) have shown promising antitumor activity with the potential to prolong survival in SCLC patients. In fact, atezolizumab when combined with chemotherapy has achieved the milestone of being the first drug to improve survival in patients with newly diagnosed extensive-stage SCLC. Other immunotherapeutic approaches evaluated in clinical trials for SCLC include the use of cytokines, cancer vaccines, antiganglioside therapies, TLR9 inhibition, anti-Notch signaling, and anti-CD47. This review discusses the rationale and clinical evidence of immunotherapy in SCLC, the conflictive clinical results of novel immunotherapeutic agents and combinatorial therapies under evaluation in SCLC patients.