Letrozole Better than Tamoxifen at Keeping Breast Cancer from Returning

May 13, 2005A phase III study led by the International Breast Cancer Study Group (IBCSG) shows that letrozole (Femara) is more effective than tamoxifen (Nolvadex) in preventing breast cancer recurrence (return of the cancer).Currently, tamoxifen is widely used to prevent breast cancer recurrence for women whose breast cancer responds to hormones. Letrozole is a different type of drug called an aromatase inhibitor, which slows or stops the growth of breast cancers that are controlled by estrogen.Doctors studied breast cancer recurrence in 8,028 postmenopausal women. These women received either tamoxifen for five years, letrozole for five years, tamoxifen for two years followed by letrozole for three years, or letrozole for two years followed by tamoxifen for five years. At this time, results are only available for the first two groups (tamoxifen only and letrozole only); follow-up is ongoing to determine if switching drugs mid-course affects breast cancer recurrence.The results showed that women who took letrozole had fewer recurrences (351) than women who took tamoxifen (428), which was a 19% reduction in risk. Additionally, the risk of cancer spreading to other areas of the body was lowered by 27% for the women taking letrozole.However, the two drugs had different side effects. Women who took tamoxifen were more likely to have blood clots, vaginal bleeding, and uterine cancer than the women who took letrozole. Those on letrozole were more likely to experience joint pain, bone fractures, and slightly increased cholesterol levels. Deadly strokes and heart attacks were more common in the letrozole group, although these conditions were rare."Our results suggest that using an aromatase inhibitor for the treatment of hormonally responsive breast cancer lowers the rate of recurrence," said Beat J. Thürlimann, MD, senior lecturer in Medical Oncology at the University of Basel in Switzerland, and Study Chairman of the trial. "The role of tamoxifen in breast cancer treatment is likely to become limited as studies continue to show that aromatase inhibitors are more effective for many patients with this disease." However, doctors noted that the side effects of each drug should be considered when determining which one is better.What this means for patientsThis study shows that letrozole, an aromatase inhibitor, is better at preventing breast cancer recurrence than tamoxifen. This study confirms other studies showing that aromatase inhibitors (such as anastrozole [Arimidex] and exemestane [Aromasin]) can reduce the risk of recurrence. However, because of the possibility of an increased risk of heart attack and stroke, more research is needed to study the long-term effects of letrozole. Given that each drug has a different set of side effects, women should discuss with their doctors which drug is best for them in preventing breast cancer recurrence based on their personal circumstances.