Season of diagnosis is associated with overall survival in patients with diffuse large B-cell lymphoma but not with Hodgkin's lymphoma - A population-based Swedish Lymphoma Register study.

OBJECTIVE AND METHODS: The aim of this study was to investigate the effect of season of diagnosis on the outcome of patients with diffuse large B-cell lymphoma (DLBCL) and Hodgkin lymphoma (HL). In this study, we included curatively treated DLBCL (n = 5875) and HL (n = 1693) patients, diagnosed between 2000 and 2011, based on data from the Swedish Lymphoma Register.

RESULTS: Overall survival was significantly better for patients diagnosed with DLBCL during the summer months, but not for patients diagnosed with HL. The difference remained in a multivariable analysis adjusted for age, stage, performance status, number of extra nodal sites and year of diagnosis (HR 1.08; 95% CI 1.02-1.14, P = 0.0069). When analyzing the DLBCL patients according to gender in the multivariable model, the effect of season was shown to be restricted to male patients (HR = 1.09, 95% CI 1.01-1.17, P = 0.0269.

CONCLUSIONS: In summary, season of diagnosis was shown to have impact on overall survival in male patients with DLBCL. Possible explanations of our results are the higher vitamin D level during the summer months, the effects of sunlight on the circadian rhythm and the immune system, or the lower risk of infectious disease during the summer. Further investigations are needed to explore these hypotheses.