Growth Hormone Is Secreted by Normal Breast Epithelium upon Progesterone Stimulation and Increases Proliferation of Stem/Progenitor Cells

• Growth hormone is produced by normal breast epithelium upon progesterone stimulation
• Stem/progenitor cells express GHR and proliferate in response to GH stimulation
• Expansion of GHR-positive cells is seen in precursor lesions of breast malignancies

SummaryUsing in vitro and in vivo experimental systems and in situ analysis, we show that growth hormone (GH) is secreted locally by normal human mammary epithelial cells upon progesterone stimulation. GH increases proliferation of a subset of cells that express growth hormone receptor (GHR) and have functional properties of stem and early progenitor cells. In 72% of ductal carcinoma in situ lesions, an expansion of the cell population that expresses GHR was observed, suggesting that GH signaling may contribute to breast cancer development.

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