The National Comprehensive Cancer Network (NCCN) recently made revisions to practice guidelines, including the hormonal treatment of breast cancer. The guideline states that Arimidex® may be considered as a treatment alternative to Nolvadex® (tamoxifen) in hormone-positive, postmenopausal women with breast cancer following appropriate discussion between physician and patient regarding available data.
The NCCN consists of a panel from 18 of the nation’s most reputable cancer treatment facilities. The panel sets clinical guidelines that are continually refined and include algorithms for diagnostic procedures and treatment of cancer. The 2002 revisions include a statement that provides Arimidex® (anastrozole) as an option to Nolvadex® for hormonal treatment of breast cancer. This indication was made following the results of a large trial that directly compared Arimidex® to Nolvadex® as hormonal therapy following primary treatment (adjuvant therapy) of hormone-positive breast cancer in post-menopausal women.
Hormone receptor-positive breast cancer, referred to as estrogen receptor and/or progesterone receptor-positive cancer, is a type of cancer that is stimulated to grow by naturally occurring female hormones called estrogen and/or progesterone. Estrogen receptor-positive (ER-positive) breast cancer cells have an overabundance of specific proteins, called estrogen receptors. Circulating estrogen binds to these receptors, which facilitates replication and growth of the cell. In addition, the binding of estrogen to estrogen receptors stimulates the synthesis of progesterone receptors. For patients with progesterone receptor-positive (PR-positive) breast cancer, progesterone that binds to the progesterone receptors also facilitates cellular replication. Currently, many women with ER and/or PR-positive breast cancer are treated with drugs that either inhibit estrogen synthesis in the body or block the growth stimulatory effects of estrogen.
Aromatase is the enzyme (protein) that is involved in the process through which hormones in the body are converted to estrogen. Anti-aromatase agents, such as Arimidex®, work by inhibiting aromatase. By inhibiting aromatase, the conversion process that is responsible for creating the active form of estrogen is blocked. This reduces levels of the active form of estrogen in the body so that cancer cells are depleted of necessary growth stimulation. This is in contrast to Nolvadex®, which blocks estrogen by directly binding to estrogen receptors.
The large trial that prompted a revision to the NCCN guidelines for hormonal therapy is referred to as the Arimidex®, Tamoxifen Alone or in Combination (ATAC) trial. The ATAC trial involved over 9,000 postmenopausal women with hormone-positive breast cancer and demonstrated improved cancer-free survival in patients treated with Arimidex compared to Nolvadex®. The NCCN indicates that there is no data available to determine if women currently on Nolvadex® should switch to Arimidex®. In addition, the NCCN cautions that Arimidex® is not appropriate therapy for premenopausal patients.
Reference: National Comprehensive Cancer Network. The following is a synopsis of recent revisions in the NCCN breast cancer treatment guideline. Available at http://www.nccn.org/. Accessed April 30, 2002.