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Birth intervals and breast cancer risk
A Kauppila1, P Kyyrönen, M Hinkula
1Department of Obstetrics and Gynecology, Oulu University Hospital, FI-90250 Oulu, Finland.
British Journal of Cancer
|September 10, 2009
Summary
Short birth intervals, especially less than one year between first and second births, significantly increase the risk of advanced breast cancer before age 50. A short interval after the last birth also elevates risk.
Area of Science:
- Reproductive epidemiology
- Oncology
- Women's health
Background:
- Birth intervals can influence breast cancer risk and tumor behavior.
- Grand multiparous (GM) women represent a unique population for studying pregnancy-related factors and cancer risk.
Purpose of the Study:
- To investigate the association between birth intervals and breast cancer risk in a large cohort of Finnish GM women.
- To examine the impact of both interpregnancy intervals and the interval from the last birth to cancer diagnosis on breast cancer risk.
Main Methods:
- A nested case-control study within a cohort of 29,488 Finnish GM women, including 628 with breast cancer.
- Conditional logistic regression was used to estimate relative risks (RR) for breast cancer, adjusting for age at first birth and parity.
Main Results:
- A short interval (<1 year) between the first and second birth was associated with a significantly increased risk of advanced ductal breast cancer in women under 50 (RR=5.29).
- A short interval (<3 years) from the last birth to cancer diagnosis also showed a substantially elevated risk of advanced ductal cancer (RR=4.00) compared to longer intervals (15+ years).
Conclusions:
- Short birth intervals may increase breast cancer risk due to hormonal stimulation from closely spaced pregnancies or impaired breast maturation.
- These findings highlight the importance of considering birth spacing in breast cancer risk assessment, particularly for advanced disease in younger women.
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