Breast secretion in Finnish women: a metabolic epidemiologic study.

Breast fluid was collected from 244 nonlactating Finnish women with no known breast disease and analyzed with respect to various epidemiologic and hormonal parameters commonly associated with breast cancer risk. The data obtained permit characterization of women with breast secretory ability and provide fundamental information on the hormone composition of breast fluid in a nondiseased population. No association was found between any epidemiologic variables (e.g., age, marital status, the number of pregnancies, the age of first pregnancy) and the ability to secrete a measurable amount of breast fluid. In addition, there appeared to be no correlation between prolactin and estrogen levels in serum and those in breast fluid within individual subjects. However, the median breast fluid prolactin level was approximately two-fold greater and the median breast fluid estrogen level was about six-fold greater than the corresponding serum values. It appears that breast ductal epithelial cells can actively transport both steroid and polypeptide hormones across a concentration barrier. Further metabolic epidemiologic investigations of hormones and potential carcinogens in the breast fluid from populations with high and low risks for breast cancer are suggested.