Exemestane breast cancer drug, molecular model. This drug, marketed as Aromasin, is taken orally as a treatment for breast cancer. It inhibits the production of oestrogen, a hormone that stimulates the growth of breast cancer tumours, by inhibiting the aromastase enzyme that produces oestrogen from androgen steroid hormones. As a result the drug limits the growth of tumours. It also seems effective in reducing excessive oestrogen levels in men. In this model, atoms are represented by coloured spheres; carbon is green, hydrogen is white, and oxygen is red.