A comparison of the outcomes of pulmonary versus extrapulmonary extensive-stage small cell carcinoma

Background: Extrapulmonary small cell carcinomas (EPSCCs) are rare cancers, comprising 0.1–0.4% of all cancers. The scarcity of EPSCC studies has led current treatment strategies to be extrapolated from small cell lung cancer (SCLC), justified by analogous histological and clinical features. Aims: We conducted a retrospective cohort study comparing the outcomes of extensive-stage (ES) SCLC and EPSCC. Methods: Patients diagnosed with ES SCLC or EPSCC between 2010 and 2020 from four hospitals in Sydney were identified. Patients who received active treatment and best supportive care were included. The primary endpoint was overall survival (OS), and secondary endpoints were progression-free survival (PFS) and overall response rates (ORRs). Results: Three hundred and eighty-four patients were included (43 EPSCC vs. 340 SCLC). EPSCC were of genitourinary (n = 15), unknown primary (n = 13) and gastrointestinal (n = 12) origin. Treatment modalities for EPSCC compared to SCLC included palliative chemotherapy (56% vs 73%), palliative radiotherapy (47% vs 59%) and consolidation chest radiotherapy (10% of SCLC). Overall, median OS was 6.4 versus 7 months for EPSCC versus SCLC respectively, but highest in prostate EPSCC (25.6 months). Of those who received chemotherapy (22 EPSCC vs 233 SCLC), median OS was 10.4 versus 8.4 months (HR OS 0.81, 95% confidence interval (CI): 0.5–1.31, P = 0.38); PFS was 5.4 versus 5.5 months (HR PFS 0.93, 95% CI: 0.58–1.46, P = 0.74) and ORR were 73% versus 68%. Conclusions: EPSCC and SCLC appeared to have comparable OS and treatment outcomes. However, the wide range of OS in EPSCC highlights the need for an improved understanding of its genomics to explore alternative therapeutics.