Small-cell lung cancer in the era of immunotherapy

Small-cell lung cancer represents about 13–15% of all lung cancers, accounting for more than 275,000 new cases worldwide every year (1). It is a poorly differentiated, high-grade carcinoma thought to originate from neuroendocrine-cell precursors within the bronchi. Small-cell lung cancer is strongly associated with heavy tobacco exposure and typically has a high mutation burden. To date, no targeted therapy has been proven to be effective in small cell lung cancer patients (1,2). Small-cell lung cancer has a high incidence of early metastasis. At diagnosis, about 70% of patients have extensive-stage disease, defined as the presence of metastatic disease by imaging or physical examination outside the hemithorax; the remaining 30% of patients have limited-stage disease, in which tumor involvement is confined to one hemithorax and can be treated in a tolerable radiation field.