Mammary hypertrophy is not associated with increased estrogen receptors

Estrogen promotes secondary female sex characteristics, including breast enlargement. Since excessive breast hypertrophy is unrelated to elevated serum estrogen levels, it has been postulated that the enlarged breast is a hypersensitive "target organ." At the cellular level, estrogen crosses the cell membrane, is bound to a cytoplasmic estrogen receptor (ER), and induces the formation of specific anabolic proteins. In breast cancer, this estrogen receptor is regarded as a measure of the sensitivity of the cell to estrogen. To determine if mammary hypertrophy is related to an increase in the number of estrogen receptors, we assayed breast tissue, not fat, from 25 consecutive breast reductions. The median age of patients was 26 years (17 to 77 years), with 752 gm per breast removed on average. Twenty-four percent of the patients were taking estrogens, primarily birth control bills. Cellular estrogen-receptor status was measured by a standardized cytosol extraction radioactive estradiol technique. Estrogen receptors were undetectable (less than 3 fmol/mg cytosol protein) in all patients. We conclude that estrogen receptors alone, and hence estrogen, are not a determinant in mammary hypertrophy. If the enlarged breast is a "target organ," it is by another mechanism.