Breast cancer in DES-exposed mothers: absence of association.

Reports in the popular press have suggested that exposure to diethylstilbestrol (DES) is followed by an abnormally high incidence of breast cancer. The reports were based on a reanalysis of data not considered ominous originally; and both data and analyses are summarized here. In addition, new data are presented on mothers of young women enrolled in the National DESAD Project at its Mayo Clinic Center. Among 408 women given DES, there were 8 confirmed instances of breast cancer, in comparison with an expected number of 8.1, based on breast cancer incidence rates among parous women in the local population. A previous case-control study of the possible association of antihypertensive therapy and breast cancer in the local population revealed DES exposure in 10% of the breast cancer group and 12% of the controls. These apparently negative results clearly indicate a need of further studies of the alleged effect of DES.