LETRAKAST Tablets LETRAKAST contains Letrozole, a potent non-steroidal aromatase inhibitor. Letrozole competitively binds to the heme subunit of the cytochrome P450 unit of the aromatase enzyme, inhibiting the conversion of adrenal androgens (androstenedione and testosterone) into estrogens (estrone and estradiol) in peripheral tissues. By eliminating systemic estrogen synthesis, letrozole deprives hormone-receptor-positive breast cancer cells of the trophic signals required for cell proliferation and tumor survival. LETRAKAST is indicated for first-line treatment of postmenopausal women with hormone-receptor-positive or hormone-receptor-unknown locally advanced or metastatic breast cancer, adjuvant treatment of postmenopausal women with hormone-receptor-positive early breast cancer, and extended adjuvant treatment of early breast cancer in postmenopausal women who have received 5 years of adjuvant tamoxifen therapy.