Comparison of outcomes between Hodgkin's lymphoma patients treated in and outside clinical trials: A study based on the EORTC‐Dutch late effects cohort‐linked data

Studies have shown higher survival rates for patients with Hodgkin lymphoma (HL) treated within clinical trials compared to patients treated outside clinical trials. However, endpoints are often limited to overall survival (OS). In this retrospective cohort study, we investigated the effect of trial participation on OS, the incidence of relapse, second cancer, and cardiovascular disease (CVD). The study population consisted of patients with HL, aged between 14 and 51 years at diagnosis, who started their treatment between 1962 and 2002 at three Dutch cancer centres. Patients were either included in the EORTC Lymphoma Group trials (H1–H9) or treated according to standard guidelines at the time. After adjusting for differences in baseline characteristics, trial participation was associated with longer OS (median OS: 29.4 years [95%CI: 27.0–31.6] for treatment inside trials versus 27.4 years [95%CI: 26.0–28.5] for treatment outside trials, p = .046), a lower incidence of relapse (HR = 0.79, 95%CI: 0.63–0.98, p = .036) and a higher incidence of CVD (HR = 1.49, 95%CI: 1.23–1.79, p < .001). The trial effect for CVD was present only for patients treated before 1983. No evidence of differences in the incidence of second cancer was found. Consequently, essential results from clinical trials should be implemented into standard practice without undue delay.