Estriol production rates and breast cancer.

We have infused [6,7-3H]estrone or [6,7-3H]estradiol and [4-14C]estriol into seven women who had had breast cancer and into five normal postmenopausal women. We measured the endogenous concentrations and the metabolic clearance rates of estrone, estradiol, and estriol and calculated the blood production rates for these steroids in each group. There were no significant differences between the respective measurements for each group. Our data does not support the argument that physiological amounts of estriol are protective against breast cancer development in women.