Family history of breast cancer and short‐term effects of childbirths on breast cancer risk

The long‐term protective effect of a pregnancy on breast cancer risk is preceded by a short‐term adverse effect, possibly reflecting a promoting effect of pregnancy hormones. In the present study, we explore whether a family history of breast cancer modifies time‐related effects of pregnancies, with...

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Bibliographic Details
Published in:International journal of cancer 2006-09, Vol.119 (6), p.1468-1474
Main Authors: Albrektsen, Grethe, Heuch, Ivar, Thoresen, Steinar, Kvåle, Gunnar
Format: Article
Language:English
Subjects:
Adult
Aged
Biological and medical sciences
breast cancer
Breast Neoplasms - epidemiology
Breast Neoplasms - genetics
Cohort Studies
Family Health
family history
Female
Gynecology. Andrology. Obstetrics
Humans
Incidence
Mammary gland diseases
Medical History Taking
Medical sciences
Middle Aged
Norway - epidemiology
Parity
Parturition
Pregnancy
Reproductive History
Risk Factors
Tumors
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Summary:The long‐term protective effect of a pregnancy on breast cancer risk is preceded by a short‐term adverse effect, possibly reflecting a promoting effect of pregnancy hormones. In the present study, we explore whether a family history of breast cancer modifies time‐related effects of pregnancies, with special emphasis on the transient increase in risk of breast cancer shortly after birth. Our study cohort comprises 1,067,289 Norwegian women aged 20–74 years. The mean follow‐up time was 18 years. Incidence rate ratios were estimated by Poisson regression analyses of person‐years at risk. Of the 7,377 women diagnosed with breast cancer during follow‐up, a total of 828 (11%) had a mother or a sister with breast cancer diagnosis. Women with a family history of breast cancer had a 2–3‐fold higher risk of breast cancer than did women without any affected family member, highest for those with a relative diagnosed before they were 50 years. Similar to women without a familial excess risk, increasing parity was associated with an overall protective effect among women with a familial predisposition, regardless of age at diagnosis of the relative. Whereas women with no familial excess risk experienced a transient increase in risk mainly after late age births, women with a family history of breast cancer experienced an adverse effect of pregnancies also at younger ages. The present results give further support to the hypothesis that the adverse effect of a term birth can be explained by a promoting effect of pregnancy hormones. © 2006 Wiley‐Liss, Inc.
ISSN:0020-7136
1097-0215
DOI:10.1002/ijc.22003