Breast cancer incidence in women prenatally exposed to maternal cigarette smoke.
Fetal exposure to maternal pregnancy hormones may influence future breast cancer risk and cigarette smoking is among the factors believed to alter pregnancy hormone levels. Specifically, total pregnancy estrogen levels are slightly decreased among pregnant women who smoke relative to women who do not. More pronounced reductions of pregnancy estiol (E3) and estradiol (E2) were observed among smoking women. Possibly, women prenatally exposed to maternal cigarette smoke may have reduced breast cancer risk as an adult. The National Cooperative DES Adenosis (DESAD) Project was a prospective study of the effects of prenatal DES exposure. When women were enrolled in the study from 1975 through 1981, their mothers were questioned about their health habits including cigarette smoking during their pregnancy with the study participant. Using responses to this question provided by the mothers at the start of the study, investigators were able to compare the breast cancer rates among women who were and were not prenatally exposed to maternal cigarette smoke. Investigators observed a 51% decrease in breast cancer rates among women whose mothers smoked while pregnant with them compared to women who were not prenatally exposed to maternal cigarette smoke. Daughters of women who smoked 15 or fewer cigarettes per day during the pregnancy appeared to have a 65% reduction in breast cancer rates compared to women whose mothers did not smoke during pregnancy. The adverse effects of prenatal cigarette smoke exposure far outweigh any benefit from possible reduction of breast cancer risk. These study results do, however, provide further evidence supporting the hypothesis that prenatal hormone exposure may affect future breast cancer risk.