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August 11, 2004

Effects of Estrogen-Only Treatment in Postmenopausal Women

JAMA. 2004;292(6):683. doi:10.1001/jama.292.6.684-b

To the Editor: It is possible that the results of the WHI investigation1 may be explained in part by the action of estrogen on biological factors that increase breast cancer risk in postmenopausal women.2 Oral estrogens, through their metabolic action, oppose insulin resistance. Furthermore, through their hepatocellular actions, they cause an increase in sex hormone–binding globulin level, and a decrease in insulin-like growth factor I (IGF-I) activity, due to both a reduction in IGF-I level and an increase in IGF-binding protein-1 level.2 IGF-I is a potent mitogen for breast tissue and breast cancer cells.

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