NEW YORK (Reuters Health) – Among women treated for early, endocrine-responsive breast cancer, adjuvant therapy with the aromatase inhibitor letrozole leads to better overall survival than does tamoxifen, in addition to the established improvement in disease-free survival and time to recurrence.

That conclusion comes from an analysis of data from the so-called BIG I-98 study that takes in account the crossover of patients from tamoxifen to letrozole. The results appear in the Journal of Clinical Oncology online February 14.

In their report, Dr. Marco Colleoni, of Istituto Europeo di Oncologia in Milan, Italy, and colleagues note that the trial included 4922 women who were randomly assigned to 5 years of adjuvant therapy with tamoxifen or letrozole. When the initial results were reported, 25% of women in the tamoxifen arm crossed over to letrozole.

To improve on the intention-treat-analysis, the researchers applied statistical methods to the 10 years of data since trial initiation to account for the selective crossover of patients.