Cancer Research Lab

Five years of letrozole is more effective than five years of tamoxifen as initial adjuvant therapy for postmenopausal endocrine-responsive early breast cancer, according to an updated analysis of the Breast International Group (BIG) 1-98 Study.

This study compared the outcomes of 8,010 women with early endocrine-responsive breast cancer who were randomized to receive one of four adjuvant treatment regimens for 5 years: letrozole; letrozole followed by tamoxifen; tamoxifen; or tamoxifen followed by letrozole.

Results of the primary core analysis, based on all four arms of the study, showed that letrozole was superior to tamoxifen as adjuvant therapy for early breast cancer.

In an updated analysis, published in the Journal of Clinical Oncology for February 10, the study team limited their analysis to women on the monotherapy arms, i.e., the 4,922 women who were randomly assigned to either continuous letrozole or continuous tamoxifen.

After a median follow-up period of 51 months, there were 352 disease events among 2,463 letrozole-treated women and 418 among 2,459 tamoxifen-treated women arm. This translates into a hazard ratio for an event of 0.82 (p = 0.007) with continuous letrozole versus tamoxifen.

Adverse effects with tamoxifen and letrozole were similar to previous reports, the authors note. Treatment with tamoxifen was associated with higher rates of thromboembolism, endometrial cancer, hot flashes, night sweats, and vaginal bleeding. Treatment with letrozole was associated with higher rates of skeletal and cardiac events as well as hypercholesterolemia.

Dr. Alan S. Coates of the International Breast Cancer Study Group Coordinating Center in Bern, Switzerland, and colleagues say the present updated analysis “adds to the body of data supporting a role for the inclusion of an aromatase inhibitor in the adjuvant therapy of postmenopausal women with receptor-positive early breast cancer.”