Extended adjuvant endocrine therapy in hormone dependent breast cancer: The paradigm of the NCIC-CTG MA.17/BIG 1–97 trial

Early hormone-receptor-positive breast cancer is a chronic relapsing disease that can remain clinically silent for many years. The NCIC-CTG MA.17/BIG 1–97 trial randomized disease-free early breast cancer patients who had received five years of adjuvant tamoxifen to either letrozole or placebo and was the first to demonstrate a benefit with extended endocrine therapy. MA.17/BIG 1–97 was stopped at the first interim analysis because disease free survival was strongly prolonged in the letrozole arm. Subsequent subset analyses and longer follow up have shown that this therapy improved survival across all groups, particularly among women with node-positive disease and those that were pre-menopausal at time of study enrolment. The MA.17/BIG 1–97 study should be considered a paradigm for extended adjuvant endocrine therapy in hormone-receptor-positive early breast cancer.