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Breast cancer is the leading cause of death in females between the age of 40 to 50 in the Western world.Iccreased lifetime exposure to estrogens, particularly produced in situ, is recognized as the most important factor in breast cancer development.Estrogens not only can promote cancers but the products of their metabolism may also initiate breast tumorigenesis.Aromatase, encoded by CYP1 9 gene, as well as sulfatase (STS) and 17β-hydroxysteroid dehydrogenase (HSD17b1) are involved in the in situ synthesis of estrogens.