Impact of prior cancer history on outcomes in thymoma: a propensity score, population-based study

Background: Prior cancer history is a common exclusion in thymoma trials. However, whether prior cancer impacts the survival of thymoma patients and the outcomes of clinical trials remains uncertain. The aim of this study is to identify the impact of prior cancer on outcomes in thymoma. Methods: Patients with thymoma diagnosed between 1975 to 2017 were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. Age, histologic types, and thymoma size were stratified to analyze. Propensity score matching (PSM), Kaplan-Meier methods and Cox proportional hazard models were used to analyze the prognostic effect of prior cancer on overall survival (OS). Results: A total of 3,827 thymoma patients were enrolled, of whom 13.22% had a prior cancer history. The Kaplan-Meier curves showed statistically significantly different survival before (P<0.001) and after PSM (P=0.0003). Subgroup analyses stratified by histologic types and thymoma size showed that thymoma patients with prior cancer had inferior survival. But thymoma patients with prior cancer displayed similar OS among patients older than 65 years (P=0.693). In multivariate analyses, patients with prior cancer displayed inferior OS [hazard ratio (HR) =1.39, 95% confidence interval (CI), 1.18 to 1.63]. Conclusion: Prior cancer conveys an inferior OS among patients with thymoma. But it does not affect the survival adversely in older patients thus broader inclusion trial criteria may be adopted in thymoma patients with a prior cancer history.