Researchers report in the journal Mayo Clinic Proceedings their study of postmenopausal women which supports the hypothesis that women who smoke cigarettes before first full-term pregnancy have a 20 percent increased risk of breast cancer compared with women who began smoking after the birth of their first child or were never smokers.

The study is a strong indicator of the continued need for smoking prevention messages to all, but especially ones tailored to this group of young women.

"Considering the young average age at smoking initiation, this study provides further justification for smoking prevention efforts aimed at young women," says Janet Olson, Ph.D., a Mayo Clinic Rochester researcher and the lead author of the study.

The risk estimates for women who smoked before their first pregnancy were 20 percent higher than those of nonsmokers. These levels of risk elevation are consistent with the risk levels reported from other epidemiological studies of cigarette smoking and breast cancer risk, says Olson. Women who started smoking after their first pregnancy had rates of breast cancer similar to those women who never smoked.

The researchers did not find evidence that duration of smoking or number of cigarettes smoked per day affected risk of breast cancer among the smokers.