Human mammary gland explants obtained (as far from the lesion as possible) from female patients who had undergone surgical biopsy for fibroadenoma of the breast were organ cultured in a chemically defined medium, and their hormone requirement for growth and differentiation was studied. Most of the explants that were cultured in hormone-free medium survived, while the addition of insulin gave full maintenance. Ovine prolactin (at a level of 0.2 µg/ml) plus insulin induced epithelial cell growth. The addition of bovine growth hormone to insulin and prolactin magnified their effect on the epithelium. Both estradiol alone (at a dose of 0.001 µg/ml) and progesterone alone (at a dose of 1 µg/ml) produced complete maintenance and lobuloalveolar development. The alveoli obtained with progesterone were small and empty, while those obtained with estradiol were larger and had secretion in their lumina. The addition of insulin, prolactin, growth hormone, and aldosterone to estradiol and progesterone (either alone or together) enhanced their action, giving alveoli with large, dark, oriented cells.

This procedure could be useful to a study of the action of hormones on the human mammary gland, as well as to an assessment of the effect on it that carcinogens and/or chemotherapeutic agents have, especially during induced phases of high proliferation of the mammary gland such as those created by estradiol and progesterone (as in this study).

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