Importance: Small cell lung carcinoma (SCLC) is uncommon in individuals who have never smoked (never-smokers). The related epidemiologic factors and prognosis remain unclear.
Objective: To assess the epidemiologic factors, clinical characteristics, and outcomes of SCLC in never-smokers.
Design, setting, and participants: A retrospective cohort study was conducted using data from the national Taiwan Cancer Registry, which was inaugurated in 1979 and maintains standardized records of patients' characteristics and clinical information for all individuals with cancer. Patients with cytologically or pathologically proven lung cancer were included for analysis. The study obtained data on patients from January 1, 1996, to December 31, 2018; data analysis was conducted from January 1, 1996, to December 31, 2019.
Exposures: Clinical characteristics and outcomes of smokers and never-smokers with SCLC.
Main outcomes and measures: Clinical characteristics for comparison included age at diagnosis, sex, performance status, tumor stage, and treatment. The main outcome parameter was overall survival of patients with SCLC from 2011 to 2018.
Results: From 1996 to 2018, a total of 225 788 patients had diagnosed lung cancer; 141 654 patients (62.7%) were men; mean (SD) age was 67.55 (12.58) years. The numbers of both patients with newly diagnosed lung cancer and those with SCLC increased until 2009 by 111.5% for lung cancer and 118.5% for SCLC. Thereafter, lung cancer cases grew in number, but SCLC cases did not; hence, the percentage of patients with SCLC decreased from 9.3% in 2009 to 6.3% in 2018. From 2011 to 2018, the percentage of never-smokers increased significantly among all patients with lung cancers (from 49.9% in 2011 to 60.2% in 2018) and among those with lung adenocarcinomas (from 64.1% in 2011 to 70.9% in 2018) (both P < .001). However, the percentage of never-smokers appeared to vary little in the SCLC population: 15.5% in 2011 and 16.1% in 2018 (P = .28). The median overall survival was significantly longer in patients with adenocarcinoma vs SCLC (adjusted hazard ratio, 0.32; 95% CI, 0.31-0.33; P < .001). Compared with smokers with SCLC, never-smokers with SCLC tended to include more older patients (age ≥70 years: 492 [57.3%] vs 2242 [44.8%]), more women (274 [31.9%] vs 322 [6.4%]), more individuals with a poor performance status (Eastern Cooperative Oncology Group performance status ≥2: 284 [33.1%] vs 1261 [25.2%]) and stage IV cancer (660 [76.9%] vs 3590 [71.8%]), and more patients without treatment (203 [23.7%] vs 626 [12.5%]). Furthermore, never-smokers, particularly men, experienced a shorter survival rate (adjusted hazard ratio, 1.10; 95% CI, 1.00-1.20; P = .04) compared with the other groups.
Conclusions and relevance: The findings of this cohort study suggest that the decrease in the percentage of patients with SCLC was associated with increased lung cancers of other histologic types, with no substantial decrease in the number of those with SCLC.