According to the results of a study published in the Annals of Oncology, adjuvant (post-surgery) treatment of hormone receptor-positive, postmenopausal breast cancer with the aromatase inhibitor Femara® (letrozole) resulted in fewer early recurrences than treatment with tamoxifen.
Each year breast cancer is diagnosed in over 200,000 women in the U.S. alone. Many of these breast cancers will be hormone receptor-positive, meaning that they are stimulated to grow by the circulating female hormones estrogen or progesterone.
Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen. These therapies include tamoxifen as well as agents known as aromatase inhibitors. Tamoxifen acts by blocking estrogen receptors, whereas aromatase inhibitors suppress the production of estrogen.
In order to compare the aromatase inhibitor Femara to tamoxifen as adjuvant therapy in women with early breast cancer, researchers conducted a Phase III clinical trial (the BIG 1-98 trial) among 8,010 postmenopausal women with operable, hormone receptor-positive breast cancer. Women were randomly assigned to one of the following four treatment regimens:
- Five years of tamoxifen
- Five years of Femara
- Two years of tamoxifen followed by three years of Femara
- Two years of Femara followed by three years of tamoxifen
In the current analysis, researchers focused specifically on early breast cancer recurrences (recurrences occurring during the first two years of treatment). A goal of the analysis was to determine whether particular subgroups of patients benefited more than others from initial treatment with Femara.
- An early breast cancer recurrence occurred in 3.1% of women treated with Femara and 4.4% of the women treated with tamoxifen.
- A benefit of Femara over tamoxifen was observed in most subgroups of women, but there was a suggestion that Femara may provide greater than average reduction in risk among women with poor prognostic factors (four or more involved lymph nodes, tumor larger than 2 cm, and vascular invasion).
The researchers conclude that as initial hormone therapy, Femara results in fewer early breast cancer recurrences than tamoxifen. There was some suggestion that women at high risk of recurrence may derive the most benefit from a hormonal therapy regimen that starts with Femara.
 The Breast International Group (BIG) 1-98 Collaborative Group. A comparison of letrozole and tamoxifen in postmenopausal women with early breast cancer. New EnglandJournal of Medicine. 2005;353:2747-57.
 Coates AS, Keshaviah A, Thürlimann B et al. Five years of letrozole compared with tamoxifen as initial adjuvant therapy for postmenopausal women with endocrine-responsive early breast cancer: update of study BIG 1-98. Journal of Clinical Oncology [early online publication]. January 2, 2007.
 Mauriac L, Keshaviah A, Debled M et al. Predictors of early relapse in postmenopausal women with hormone receptor-positive breast cancer in the BIG 1-98 trial. Annals of Oncology. 2007;18:859-867.