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Title: Intrauterine environments and breast cancer risk: meta-analysis and systematic review (Review).
Author: Park SK, Kang D, McGlynn KA, Garcia-Closas M, Kim Y, Yoo KY, Brinton LA
Journal: Breast Cancer Res 10(1):R8-R8
Year: 2008
Month: January

Abstract: ABSTRACT: INTRODUCTION: Various perinatal factors, including birth weight, birth order, maternal age, gestational age, twin status and parental smoking have been postulated to affect breast cancer risk in daughters by altering the hormonal environment of the developing fetal mammary glands. Despite ample biological plausibility, epidemiological studies to date have provided conflicting results. We investigated the associations between perinatal factors and subsequent breast cancer risk through meta-analyses. METHODS: We reviewed breast cancer studies published from January 1966 to February 2007 that included data on birth weight, birth order, maternal age, gestational age, twin status, and maternal or paternal smoking. Meta-analyses using random-effect models were employed to summarize the results. RESULTS: We found that heavier birth weights were associated with increased breast cancer risk, with studies involving 5 categories showing ORs of 1.24 (95% CI, 1.04-1.48) for 4000 g or more and 1.15 (1.04-1.26) for 3500-3999 g, relative to 2500-2599 g. These studies provided no support for a J-shaped relationship of birthweight to risk. Support for an association with birthweight also derived from studies based on 3 birth weight [OR=1.15 (95% CI, 1.01-1.31) for greater than or equal to 4000 g, relative to < 3000 g] and 2 birth weight [OR=1.09 (95% CI, 1.02-1.18) for greater than or equal to 3000 g, relative to < 3000 g] categories. Women born to older mothers and twins were also at some increased risk, but results were heterogeneous across studies and publication years. Birth order, prematurity, and maternal smoking were unrelated to breast cancer risk. CONCLUSION: Our findings provide some support for the hypothesis that in utero exposures reflective of higher endogenous hormone levels could affect the development of adult breast cancer risk.