Birth intervals and breast cancer risk |
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| Authors: | A Kauppila P Kyyr?nen M Hinkula E Pukkala |
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| Affiliation: | 1Department of Obstetrics and Gynecology, Oulu University Hospital, FI-90250 Oulu, Finland;2Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Pieni Roobertinkatu 9, FI-00130, Helsinki, Finland;3School of Public Health, FI-33014 University of Tampere, Tampere, Finland |
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| Abstract: | Background: The interval between successive births (birth interval) may affect breast cancer risk, whereas interval from last birth to cancer onset may modify its behaviour.Methods: The study cohort consisted of 29 488 Finnish grand multiparous (GM) women, including 628 women with breast cancer. Conditional logistic regression for case–control design nested within the cohort was used to estimate proportional hazards (referred as relative risks, RR). Age at first birth and parity were co-variables.Results: Short interval (<1 year) between first and second birth increased the risk of advanced ductal breast cancer at ages < 50 years (RR=5.29; 95% CI 2.00–14.0) as compared to interval 3+ years. The risk of advanced ductal cancer was also large (RR = 4.00; 95% CI 1.19–13.4) shortly (<3 years) after last birth as compared with the period 15+ years.Conclusions: Short birth interval-associated excess breast cancer risk may be related to stimulatory effects of female steroid hormones produced during two closely connected pregnancies, or defective breast maturation owing to failures in breastfeeding. |
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| Keywords: | aetiology of breast cancer risk factor pregnancy age at first birth birth interval interval from birth to cancer |
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