Evaluation of the Risk of Relapse in Classical Hodgkin Lymphoma at Event-Free Survival Time Points and Survival Comparison With the General Population in British Columbia

Studies in classical Hodgkin lymphoma (cHL) typically measure the time to events from diagnosis. We evaluated the risk of relapse at event-free survival time points in cHL and compared the risk of death to expected mortality rates in British Columbia (BC). The BC Cancer Agency Lymphoid Cancer Database was screened to identify all patients age 16 to 69 years diagnosed with cHL between 1989 and 2012 treated with the chemotherapy regimen of doxorubicin, bleomycin, vinblastine, and dacarbazine (or equivalent). We compared the observed mortality to the general population using age-, sex-, and calendar period-generated expected mortality rates from BC life-tables. Relative survival was calculated using a conditional approach and expressed as a standardized mortality ratio of observed-to-expected deaths. One thousand four hundred two patients were identified; 749 patients were male (53%), the median age was 32 years, and 68% had advanced-stage disease. The median follow-up time was 8.4 years. Seventy-two percent of relapses occurred within the first 2 years of diagnosis. For all patients, the 5-year risk of relapse from diagnosis was 18.1% but diminished to 5.6% for patients remaining event free at 2 years. For advanced-stage patients who were event free at 2 years, the 5-year risk of relapse was only 7.6%, and for those who were event free at 3 years, it was comparable to that of limited-stage patients (4.1% v 2.5%, respectively; P = .07). Furthermore, international prognostic score ≥ 4 and bulky disease were no longer prognostic in patients who were event free at 1 year. Although the relative survival improved as patients remained in remission, it did not normalize compared with the general population. Patients with cHL who are event free at 2 years have an excellent outcome regardless of baseline prognostic factors. All patients with cHL had an enduring increased risk of death compared with the general population.