Pregnancy and breast cancer: A possible explanation for the negative association

We propose that pregnancy protects against breast cancer, in part, because it results in excretion of lipophilic carcinogens by the mother through the fetal fat and vernix caseosa. We review several lines of epidemiologic and toxicologic evidence in support of this idea, including concordances between known or suspected risk factors for cancer of the female breast and known or suspected risk factors for increased body burdens of lipophilic carcinogens.