Letrozole chemotherapy drug molecule. Computer model of a molecule of the chemotherapy drug letrozole (marketed as Femara). Atoms are represented as spheres and are colour-coded: carbon (pink), hydrogen (white) and nitrogen (yellow). Letrozole is used to treat breast cancer in post-menopausal women. It belongs to a class of drugs called aromatase inhibitors. These drugs stop the production of oestrogen, a hormone responsible for the growth and recurrence of many breast cancers in post-menopausal women. Letrozole is also used in fertility treatment to induce ovulation.