Exemestane breast cancer drug. Computer model of a molecule of the breast cancer drug exemestane. 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. The molecule's chemical formula is C20.H24.O2. The atoms are shown as colour-coded spheres in this space-filled model: carbon (blue), hydrogen (yellow), and oxygen (red).