Background Vitamin D has been suggested to influence the incidence and prognosis of breast cancer, and studies have found better overall survival (OS) after diagnosis for breast cancer in summer–autumn, where the vitamin D level are expected to be highest.
Objective To compare the prognostic outcome for early breast cancer patients operated at different seasons of the year.
Design Open population-based cohort study.
Setting Danish women operated 1978–2010.
Cases 79 658 adjusted for age at surgery, period of surgery, tumour size, axillary lymph node status and hormone receptor status.
Statistical analysis The association between OS and season of surgery was analysed by Cox proportional hazards regression models, at survival periods 0–1, 0–2, 0–5 and 0–10 years after surgery. A two-sided p value <0.05 was considered statistical significant.
Results Only after adjustment for prognostic factors that may be influenced by vitamin D, 1-year survival was close to significantly associated season of surgery. 2, 5 and 10 years after surgery, the association between OS and season of surgery was not significant.
Limitations Season is a surrogate measure of vitamin D.
Conclusions The authors found no evidence of a seasonal variation in the survival after surgery for early breast cancer. Lack of seasonal variation in this study does not necessarily mean that vitamin D is of no importance for the outcome for breast cancer patients.
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To cite: Teilum D, Bjerre KD, Tjønneland AM, et al. Breast cancer survival and season of surgery: an ecological open cohort study. BMJ Open 2012;2:e000358. doi:10.1136/bmjopen-2011-000358
Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests All authors have completed the ICMJE disclosure form (available on request from the corresponding author) and declare: no support from any organisation for the submitted work, no financial relationships with any organisations that might have an interest in the submitted work in the previous 3 years and no other relationships or activities that could appear to have influenced the submitted work.
Ethics approval The data are from Danish Breast Cancer Group.
Contributors DT contributed to conception and interpretation of data, reviewed the literature, drafted the article and finally approved the submitted paper. KDB analysed and interpreted the data, drafted the statistical part and finally approved the submitted paper. AMT and NK contributed to the interpretation of data, revised it critically for important intellectual contents and finally approved the submitted paper.
Provenance and peer review Not commissioned; externally peer reviewed.
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