Placenta size may affect breast cancer risk

The heavier the placenta during pregnancy, the greater a woman's risk of breast cancer before menopause, a Swedish study suggests. "Compared with mothers whose placenta at first delivery weighed less than 500 grams, women whose placenta weighed equal to or greater than 700 grams had a 38 percent increase in risk of breast cancer," said study author Dr. Sven Cnattingius, a professor at the Karolinska Institute in Stockholm. Results of the study are published in the Nov. 16 issue of the Journal of the American Medical Association. While scientists don't know the exact cause of breast cancer, hormones clearly play a role in risk, according to Cnattingius. And during pregnancy, he added, hormone levels surge. "Hormones during pregnancy are primarily produced by the placenta. And the levels of, for example, estriol -- the most potent estrogen -- are reported to increase with placental weight. We therefore hypothesized that a mother's risk of breast cancer may increase with placental weight," said Cnattingius. The placenta is the temporary organ that supplies nourishment to the fetus. To test this hypothesis, the researchers reviewed data from more than 300,000 Swedish women included in the Sweden Birth Register from 1982 through 1989. The study included follow-up information on the women through 2001, or until they had been diagnosed with breast cancer or died. Fewer than 1 percent of the women -- 2,216 -- developed breast cancer. Almost all of the women -- 95 percent -- were diagnosed before the age of 50. The study confirmed the researchers' hypothesis. Women whose placentas weighed 700 grams or more had a 38 percent increased risk of breast cancer, compared to women whose placentas weighed less than 500 grams, according to the study. A woman with a placenta weighing between 500 and 699 grams in one pregnancy and 700 grams or more in another pregnancy had an 82 percent increased risk of breast cancer, compared to read more