Growth regulation of human breast carcinoma occurs through regulated growth factor secretion

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Abstract
We describe studies on human breast cancer in which it is shown that specific growth factors (IGF‐I, TGFα, PDGF) are secreted by human breast cancer cells and likely to be involved in tumor growth and progression. These activities are regulated by estradiol in hormone‐dependent breast cancer and secreted constitutively by hormone‐independent cells. These growth factor activities can induce the growth of hormone‐dependent cells in vivo in athymic nude mice. Hormone‐dependent breast cancer cells also secrete TGFβ, a growth‐inhibitory substance, when treated with antiestrogens. TGFβ functions as a negative autocrine growth regulator and is responsible for some of the growth‐inhibitory effects of antiestrogens.