Objectives: Season of birth has been associated with adult morbidity and mortality, but few epidemiologicalstudies have examined whether season of birth contributes to the development of cancer. Using data fromthe Australian National Endometrial Cancer Study, a population-based case-control study of 1399 cases and1539 controls, we examined the association between season of birth and risk of endometrial cancer. Methods:Unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI)for the association between season of birth and endometrial cancer. Additional analyses were stratified by stateof birth. Results: Season of birth was not associated with endometrial cancer overall, but there was an increasedrisk among women born in summer in Tasmania, the most southerly state (OR = 4.46, 95% CI: 1.24-16.06) andnon-significant increases in the other southern states. Conclusion: Further data are required to confirm thesefindings, however the observed associations may be due to the longer days and/or greater hours of sunshine inAustralia’s southerly states in summer, suppressing melatonin levels in summer-born infants and predisposingthem to cancer in adulthood.
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