I. Introduction II. Aromatase Cytochrome P450 and in Situ Estrogen Production III. Aromatase in Breast Cancer A. Introduction B. Localization C. Genetic regulation D. Clinical and pathological correlation E. Male breast cancer IV. Aromatase in Endometrial Cancer A. Introduction B. Localization C. Genetic regulation D. Clinical and pathological correlation V. Aromatase in Ovarian Cancer A. Introduction B. Localization C. Genetic regulation D. Clinical and pathological correlation VI. Summary