Aromasin is a drug in a class of medications known as aromatase inhibitors. Aromasin is used in treating early breast cancer among women who have reached postmenopausal stage. Aromasin lowers estrogen levels in the body, which slows down or stops the growth of some types of breast tumors. Some tumors need estrogen for them to grow in body. Aromasin is often administered in women whose cancerous tumor continues to progress even after they have had surgery, radiation, and other forms of medication without success.