Birth weight and breastfeeding in infancy may affect premenopausal breast cancer risk

05/19/05

BUFFALO, N.Y. -- Premenopausal women who were heavier than average at birth or had not been breastfed as infants appear to be at increased risk for developing breast cancer, epidemiologists at the University at Buffalo's School of Public health and Health Professions have found. Results of the study, which showed no association between birth weight and breastfeeding in infancy and postmenopausal breast-cancer risk, were reported at the American Association for Cancer Research annual meeting in Anaheim, Calif.

"The intrauterine and neonatal life periods have been suggested as critical windows in mammary gland development," said Maddalena Barba, M.D., research instructor in the UB Department of Social and Preventive Medicine and lead researcher on the study. "In utero and early childhood exposures might affect breast cancer risk by altering the hormonal environment of the developing fetus and young infant through mechanisms not yet completely clarified."

Barba and colleagues from UB's School of Public Health and Health Professions analyzed data collected from 2,382 women participating in the Western New York Exposures and Breast Cancer Study conducted from 1996-2001 during in-person, computer-assisted interviews. Complete information on the exposures of interest was available for 845 participants newly diagnosed with breast cancer during the study period who served as cases, and for 1,573 matched controls.

Researchers compared cases and controls, taking into consideration already well-recognized breast-cancer risk factors such as age, education, body-mass index, history of benign breast disease, family history of cancer, months of lactation, age at first menstrual period, age at first pregnancy, number of pregnancies and age at menopause for postmenopausal women.

Results showed that premenopausal women whose birth weight was greater than 8.5 pounds, and premenopausal women who had not been breast fed as infants, had an almost two-fold risk of developing breast cancer when compared to premenopausal women whose weight at birth was 5.5-7 pounds (reference category) and who had been breast fed.

None of these variables showed a relationship with postmenopausal breast cancer. Birth order was not associated with breast cancer risk in pre- or postmenopausal women.

"Our results support the hypothesis that early life events impact women's breast-cancer risk later in life," said Barba. "Further research based on targeted studies is needed to reach a deeper understanding of the underlying biological mechanisms."

Source: Eurekalert & others

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