CYP19A1 and breast cancer: Hormonal therapy such as selective oestrogen receptor modulators, aromatase inhibitors and gonadotropin-releasing hormone analogue are used in oestrogen-dependent breast cancers through the inhibition of the oestrogen signalling pathway or blocking the biosynthesis of androgens by inhibition of aromatase enzyme, resulting in a reduction in oestrogen levels or inhibition of oestrogen production, respectively.