CYP19A1 and breast neoplasm: Although the exact localization of aromatase in human breast tumor is still controversial [37,38], in majority of the breast cancer cases aromatase activity and aromatase mRNA levels show higher levels than those observed in non-malignant mammary tissues [39]; this supports the concept that in-situ production of E2 by aromatase plays a major role in breast cancer progression [40].