Abstract: Objective To investigate the relevant factors influencing the prognosis of patients with primary small cell carcinoma of the esophagus (PSCCE), providing valuable insights for clinical treatment decision-making. 
Methods This study collected data from the Surveillance, Epidemiology, and End Results (SEER) database and single-center registries in China. A total of 230 PSCCE patients diagnosed between 2000 and 2020 were included (SEER: 158; China: 72). Kaplan-Meier analysis was used to plot survival curves, Log-Rank test was used for survival comparison, and Cox proportional hazards regression was applied to evaluate prognostic factors. 
Results Both univariate and multivariate Cox regression analyses revealed chemotherapy as an independent prognostic factor for overall survival (OS). In the SEER cohort, the hazard ratio (HR) in the chemotherapy group was 0.395 (95%CI: 0.261-0.597, P＜0.001), and the median survival time (MST) for the chemotherapy group was 12 months, which was significantly longer than 3.5 months in the non-chemotherapy group (P＜0.001). In the Chinese cohort, the HR for chemotherapy was 0.399 (95%CI: 0.177-0.899, P=0.027), with MST of 22.6 months and 9.8 months for the chemotherapy and non-chemotherapy groups respectively (P＜0.001). Subgroup analysis demonstrated the protective effect of chemotherapy in limited-stage patients. For the SEER cohort, the HR for chemotherapy in limited-stage patients was 0.416 (95%CI: 0.236-0.735, P=0.003), with MST of 16 months vs. 5.5 months for the chemotherapy and non-chemotherapy groups respectively (P＜0.001). For the Chinese 〖JP2〗cohort, the HR for chemotherapy in limited-stage patients was 0.345 (95%CI: 0.157-0.760, P=0.008),〖JP〗 with MST of 23.6 months vs. 9.8 months for the chemotherapy and non-chemotherapy groups respectively (P＜0.001). Treatment comparison showed that in the SEER cohort, the MST of the chemoradiotherapy combined with surgery group was significantly longer than that of the chemotherapy-alone group (18 months vs. 10 months, P=0.009). In the Chinese cohort, the MST of the surgery combined with chemotherapy group was significantly longer than that of the surgery-alone group (25.8 months vs. 10 months, P＜0.001).
Conclusion Chemotherapy emerges as the only common prognostic factor shared by PSCCE patients in both China and the United States, establishing itself as a pivotal component within multidisciplinary treatment approaches. For limited-stage patients, it′s also crucial to acknowledge the significance of chemotherapy, emphasizing preference for combination regimens that incorporate chemotherapy. 

Key words: esophageal neoplasms, SEER database, prognosis