Letrozole (INN, trade name Femara), It is an oral non-steroidal aromatase inhibitor. It has been introduced for the treatment of hormonally-responsive breast cancer. It is used to treat breast cancer in women. Estrogens are produced by the conversion of androgens through the activity of the aromatase enzyme.t is also used for women who have already had other treatment of cancer. Some of the female hormones that occur naturally in the body are the cause can increase the growth of some breast cancer.