Women who gain more than 38 pounds during pregnancy may face a risk of developing postmenopausal breast cancer that is 40% greater than that of women who gain less weight. By contrast, weight gain during pregnancy appears to have no effect on the risk of developing premenopausal breast cancer. The findings, reported at the annual meeting of the American Association for Cancer Research, are based on a study of Finnish women conducted by an international group of researchers from Washington, D.C. and Finland.

"We also found that women who retain the added pounds after pregnancy are at the greatest risk. These additional pounds may induce changes in breast tissue that increase susceptibility to breast cancer in later life," explained Leena Hilakivi-Clarke, Ph.D., of the Lombardi Cancer Center at Georgetown University, one of the study's principal investigators. However, she cautioned that overall the increased risk due to pregnancy weight gain is modest-equivalent to the increased risk from obesity after menopause.

Hilakivi-Clarke noted that weight gain of 25 to 35 pounds is recommended during pregnancy and is not associated with an increase in risk for either premenopausal or postmenopausal breast cancer. Eight out of 10 women who develop breast cancer have no known risk factors.

The study, based on an analysis of data from more than 27,000 women in Finland, adds another piece to the complex puzzle of the relationship among pregnancy, estrogen levels, and breast cancer risk.

Hilakivi-Clarke and colleagues in Finland examined the relationship between pregnancy weight gain and breast cancer risk in two cohorts of Finnish women. The first cohort, consisting of more than 17,360 women, included 98 women who developed premenopausal breast cancer at an average age of 47. The second cohort of 3,209 women included 185 who developed postmenopausal breast cancer at an average age of 58.

"At least one previous study has shown that women who gain the most weight during pregnancy have higher estrogen levels than women who gain less weight," said Hilakivi-Clarke. "Women who have the highest estrogen levels during pregnancy are more prone to develop breast cancer."

SOURCE:
93rd Annual Meeting of the American Association for Cancer Research, April 9, 2002, San Francisco, CA