Birth Characteristics and Subsequent Risk for Breast Cancer in Very Young Women

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Abstract
There is growing evidence that prenatal exposures may influence later breast cancer risk. This matched case-control study used linked New York State birth and tumor registry data to examine the association between birth characteristics and breast cancer risk among women aged 14–37 years. Cases were women diagnosed with breast cancer between 1978 and 1995 who were also born in New York after 1957 (n = 484). For each case, selected controls were the next six liveborn females with the same maternal county of residence. The authors found a J-shaped association between birth weight and breast cancer risk, and very high birth weight (≥4,500 g) was associated with the greatest elevation in risk (adjusted odds ratio (OR) = 3.10, 95% confidence interval (CI): 1.18, 7.97). The association of maternal age with breast cancer risk was also J-shaped, with maternal age of more than 24 years showing a positive, linear association (adjusted OR = 1.94, 95% CI: 1.18, 3.18 for maternal age ≥35 vs. 20–24 years; p for trend = 0.02). In contrast, women born very preterm had a lower risk (adjusted OR = 0.11, 95% CI: 0.02, 0.79 for gestational age <33 vs. ≥37 weeks). These findings support a role for early life factors in the development of breast cancer in very young women.