Further evidence that prenatal hormone exposure may affect future breast cancer risk

Breast cancer incidence in women prenatally exposed to maternal cigarette smoke

2005 Study Abstract

BACKGROUND
Clinical studies show that maternal cigarette smoking reduces pregnancy estrogen levels. Women prenatally exposed to maternal cigarette smoke may, therefore, have a lower breast cancer risk because the fetal mammary gland’s exposure to maternal estrogen is decreased. Associations between prenatal maternal cigarette smoke exposure and breast cancer, however, have not been observed in previous case-control studies that relied on exposure assessment after the onset of cancer. At the start of this study, cigarette smoking history was obtained directly from the mother.

METHODS
The National Cooperative DES Adenosis project was a follow-up study of health outcomes in women prenatally exposed to diethylstilbestrol (DES). At the start of the study, women’s mothers provided information about cigarette smoking habits during the time they were pregnant with the study participant. In the current study, the breast cancer rates are compared among 4031 women who were or were not prenatally exposed to maternal cigarette smoke. The resultant relative rate (RR) is adjusted for potential confounding by other breast cancer risk factors using Poisson regression modeling.

RESULTS
Fetal exposure to maternal cigarette smoke appeared to be inversely associated with breast cancer incidence (RR = 0.49; 95% confidence interval [CI] = 0.24-1.03). The inverse association was more apparent among women whose mothers smoked 15 cigarettes or fewer per day than among daughters of heavier smokers. There were, however, too few cases to precisely estimate a possible dose-response relationship.

CONCLUSION
These results support the hypothesis that in utero exposure to maternal cigarette smoke reduces breast cancer incidence

DES Follow-up Study

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.

Sources

DES DIETHYLSTILBESTROL RESOURCES

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