title: 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.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Oncology, Skane University Hospital, Lund, Sweden. erzsebet.szekely@med.lu.se.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Székely
authors.affiliation: Department of Oncology, Skane University Hospital, Lund, Sweden.
authors.forename: Ola
authors.initials: O
authors.lastname: Lindén
authors.affiliation: Regional Cancer Centre, Lund, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Peterson
authors.affiliation: Department of Oncology, Skane University Hospital, Lund, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Jerkeman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006689:Hodgkin Disease / Q000175:diagnosis / Q000453:epidemiology* / Q000401:mortality / Q000628:therapy; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000175:diagnosis / Q000453:epidemiology* / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009367:Neoplasm Staging; D011159:Population Surveillance; D016016:Proportional Hazards Models; D012042:Registries; D012189:Retrospective Studies; D012621:Seasons; D013548:Sweden / Q000453:epidemiology; D061665:Time-to-Treatment; D055815:Young Adult
keywords: diffuse large B-cell lymphoma; gender; seasonal variation