Inner Banner



CAS Number: 112809-51-5

Formula: C17H11N5

Molecular Weight: 285.3 g/mol

Method of Analysis: Based on: USP

Application: Breast Cancer (Post-menopausal Estrogen-receptor-positive) Letrozole is an oral non-steroidal aromatase inhibitor used for the treatment of hormonally-responsive breast cancer after surgery.


The growth of some cancers of the breast is stimulated or maintained by estrogens. In postmenopausal women, estrogens are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens (primarily androstenedione and testosterone) to estrone and estradiol. The suppression of estrogen biosynthesis in peripheral tissues and in the cancer tissue itself can therefore be achieved by specifically inhibiting the aromatase enzyme. Letrozole is a nonsteroidal competitive inhibitor of the aromatase enzyme system; it inhibits the conversion of androgens to estrogens. In adult nontumor- and tumor-bearing female animals, letrozole is as effective as ovariectomy in reducing uterine weight, elevating serum LH, and causing the regression of estrogen-dependent tumors. In contrast to ovariectomy, treatment with letrozole does not lead to an increase in serum FSH. Letrozole selectively inhibits gonadal steroidogenesis but has no significant effect on adrenal mineralocorticoid or glucocorticoid synthesis. Letrozole inhibits the aromatase enzyme by competitively binding to the heme of the cytochrome P450 subunit of the enzyme, resulting in a reduction of estrogen biosynthesis in all tissues.

Storage conditions: preserved in tight containers at controlled room temperature.

Packaging: 1th polyethylene plastic bag. 2th. Three layered aluminum foil.