SAN FRANCISCOWomen who gain 38 lb or more during pregnancy have a 40% greater risk of postmenopausal breast cancer than women who gain less weight, Leena Hilakivi-Clarke, PhD, said at the 93rd Annual Meeting of the American Association for Cancer Research (abstract 1169).
Weight gain during pregnancy, however, appears to have little effect on the risk of premenopausal breast cancer, said Dr. Hilakivi-Clarke, professor of oncology, Georgetown University.
In the study, done in collaboration with Riitta Luoto, MD, of the University of Tampere, Finland, researchers analyzed data from more than 27,000 women in Finland.
The first cohort, consisting of more than 17,360 women, contained 392 women who served as controls and 98 women who developed premenopausal breast cancer at an average age of 47. Breast cancer diagnosis and pregnancy weight gain were obtained from a questionnaire the study participants filled out from 1990 to 1993.
The second cohort of 4,090 women, included controls and 166 women who developed postmenopausal breast cancer at the mean age of 68.3 years. These breast cancer cases were identified through the Finnish cancer registry; pregnancy weight gain was obtained from cards stored in maternity centers.
"We found that women who gained the most weight during pregnancy are at higher risk for postmenopausal breast cancer," Dr. Hila-kivi-Clarke said. "Those who retained the added pounds after pregnancy are also at risk. Overall, the increased risk due to pregnancy weight gain is modest and similar to the increased risk from obesity after menopause."
Her research team has not yet investigated whether women who gain too much weight during pregnancy, and then lose all the weight, have an increased risk of postmenopausal breast cancer.