Anastrozole is a non-steroidal aromatase inhibitor used to decrease circulating estrogen levels in the treatment of postmenopausal women with estrogen-responsive breast cancer. Aromatase inhibitors, including anastrozole, have become endocrine drugs of choice in the treatment of postmenopausal breast cancer due to a more favourable efficacy and adverse effect profile as compared to earlier estrogen receptor modulators such as tamoxifen..