A nonsteroidal inhibitor of estrogen synthesis that resembles paclitaxel in chemical structure. As a third-generation aromatase inhibitor, anastrozole selectively binds to and reversibly inhibits aromatase, a cytochrome P-450 enzyme complex found in many tissues including those of the premenopausal ovary, liver, and breast; aromatase catalyzes the aromatization of androstenedione and testosterone into estrone and estradiol, the final step in estrogen biosynthesis. In estrogen-dependent breast cancers, anastrozole may inhibit tumor growth. Check for "https://www.cancer.gov/about-cancer/treatment/clinical-trials/intervention/C1607" active clinical trials using this agent. ("http://ncit.nci.nih.gov/ncitbrowser/ConceptReport.jsp?dictionary=NCI%20Thesaurus&code=C1607" NCI Thesaurus)