Genetic predisposition to carcinoma of the breast: Multiple human genotypes for estrogen 16 alpha hydroxylase activity in caucasians

The ratio of administered estrioVestrone or estradiol 178 modifies the uterotropic action of estrogen upon uterine growth i n spayed rodents in vivo and the binding of tritiated estrone or estradiol to uterine and mammary estrogen receptor proteins in vivo and in vitro. Caucasian women with untreated breast cancer excrete significantly lower urinary ratios of estrioVestrone + estradiol (estriol quotient, Eq) compared to age‐matched noncancerous women. Pregnancy, which induces a 10‐fold augmentation of estriol production from fetoplacental sources above that of estrone and estradiol, significantly reduces human breast cancer risk.