Study Confirms Letrozole Prevents More Breast Cancer Recurrences than Tamoxifen

Adapted from the NCI Cancer Bulletin.

After a median of 8 years of follow-up from a large randomized trial, women with estrogen receptor positive breast cancer who received 5 years of treatment with the aromatase inhibitor letrozole were less likely to have their cancer recur or to die during follow-up than women who had 5 years of treatment with tamoxifen. In addition, 5 years of sequential treatment—either 2 years of letrozole followed by 3 years of tamoxifen or 2 years of tamoxifen followed by 3 years of letrozole—was not better than 5 years of letrozole alone at preventing recurrence or death. These results, from the BIG 1-98 trial, were published online October 20, 2011 in Lancet Oncology.

Researchers from 27 countries enrolled 8,010 postmenopausal women with invasive breast cancer that could be removed surgically in the trial. After surgery, the women were randomly assigned to one of four groups: 5 years of letrozole (letrozole monotherapy), 5 years of tamoxifen (tamoxifen monotherapy), or one of the two sequential treatment groups. Novartis, the maker of letrozole, provided funding for the trial, along with NCI and the International Breast Cancer Study Group.

In 2005, preliminary results from the trial showed that letrozole alone was better than tamoxifen at preventing early recurrences, and when given the option to cross over, 619 of the 2,459 women in the tamoxifen-only arm chose to cross over to receive letrozole. Since crossover can complicate interpretation of trial results, the researchers performed a traditional intention-to-treat analysis (which includes only data from the original treatment assignments) and a type of analysis designed to account for crossover.

In the intention-to-treat analysis, women who received letrozole alone had a disease-free survival rate of 73.8 percent at 8 years, compared with a rate of 70.4 percent for women who received tamoxifen alone. Women who received letrozole alone also had better overall survival at 8 years than women receiving tamoxifen alone (83.4 versus 81.2 percent). The differences between the groups were slightly greater in the analysis accounting for the crossover. Neither of the two sequential treatments provided better results than letrozole alone.

Although these updated results show that letrozole reduces risk of relapse and improves survival compared with tamoxifen, "use of a sequence might be reasonable for patients at low-to-intermediate risk of relapse, those for whom starting or continuing letrozole is contraindicated, or in cases where 5 years of letrozole might not be available," concluded the authors.

"These two drugs have different side effects, and this study shows that a woman has options," said Jo Anne Zujewski, M.D., head of Breast Cancer Therapeutics in NCI's Division of Cancer Treatment and Diagnosis, who was not involved in the research. "If the side effects from letrozole are intolerable, benefits are maintained by switching to tamoxifen rather that stopping hormonal therapy altogether."

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