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Infants with high birth weights increased mother’s breast cancer risk
Giving birth to an infant with a high birth weight was associated with increased breast cancer risk in later life and also was linked to a hormonal environment during pregnancy favoring future breast cancer development and progression, according to study results published in PLoS ONE
Prior studies have shown that a woman’s risk for breast cancer in later life is associated with her infants’ birth weights. However, since there is correlation between a mother’s birth weight and her infants’ birth weights, it is unclear whether both are independently associated with the mother’s ensuing breast cancer risk.
“Recent animal studies have suggested that breast stem cells, which are involved in the origins of breast cancer, may increase or decrease their number in response to hormone exposures, including ones during pregnancy,” Radek Bukowski, MD, PhD, professor of obstetrics and gynecology in the division of maternal-fetal medicine at the University of Texas Medical Branch at Galveston, said in a press release. “They retain a ‘memory’ of prior hormone exposure, which could explain the increased risk of breast cancer seen following pregnancy, especially in women with a large birth weight infant. The hormones create a long-term effect that may lead to breast cancer later.”
To determine whether this association is independent of other breast cancer risk factors and to examine possible connections between infants’ birth weight and the hormonal environment during pregnancy, researchers analyzed a prospective cohort of 410 recent mothers (Framingham Study) and 23,824 pregnant women (FASTER trial).
Among the participants in the Framingham Study, researchers studied the risk for breast cancer in relation to a first infant’s birth weight, mother’s own birth weight and breast cancer risk factors. In the larger cohort of the FASTER trial, researchers measured serum concentrations of estriol, anti-estrogen alpha-fetoprotein, as well as pregnancy-associated plasma protein A, which exhibits insulin-like growth factor binding proteins typically associated with breast cancer development and progression.
According to a 14-year follow-up of the Framingham Study, 31 women (7.6%) were diagnosed with breast cancer. Women with large birth weight infants exhibited a higher breast cancer risk compared with other women (HR=2.5; 95% CI, 1.2-5.2). These results were not affected by adjustment for birth weight of the mother and traditional breast cancer risk factors (adjusted HR=2.5; 95% CI, 1.2-5.6).
Analysis of the FASTER trial revealed a strong positive relationship between the infant birth weight, both unadjusted and percentile of individual growth potential, and the mother’s serum estriol/anti-estrogen alpha-fetoprotein ratio and serum pregnancy-associated plasma protein A concentration. Adjustment for covariates associated with risk for breast cancer did not have a material effect on those associations (P<.0001).
According to Bukowski, “We also found that women delivering large babies — those in the top quintile of this study, which included babies whose weight was 8.25 or more pounds — have increased levels of hormones that create a ‘pro-carcinogenic environment.’ This means that they have high levels of estrogen, low levels of anti-estrogen and the presence of free insulin-like growth factors associated with breast cancer development and progression. Women can’t alter their pregnancy hormones, but can take steps to increase their general protection against breast cancer.”
Disclosure: The researchers report no relevant financial disclosures.