Breast cancer survival and season of surgery: an ecological open cohort study. Issue 1 (5th January 2012)

• Record Type: Journal Article
• Authors: Teilum, Dorthe; Bjerre, Karsten D; Tjønneland, Anne M; Kroman, Niels
• Is Part Of: BMJ open. Volume 2:Issue 1(2012)
• Publication Date: 2012-01-05
• Subjects: Medicine -- Research -- Periodicals; 610.72
• DOI: 10.1136/bmjopen-2011-000358
• Languages: English
• ISSNs: 2044-6055

Abstract

Abstract : 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.