Currently it is recommended that most postmenopausal women with hormone receptor–positive early stage breast cancer be treated with 5 additional years of aromatase inhibitor (AI) therapy following completion of an initial 5 years of treatment.
The optimal duration of endocrine (hormone) therapy beyond five years after initial AI adjuvant therapy for postmenopausal women with hormone receptor–positive breast cancer however is unknown. Despite the success of adjuvant endocrine therapy, 50% of all recurrences occur after the first five years, especially in hormone receptor–positive breast cancer.
In order to further evaluate the optimal duration of AI therapy a clinical trial was designed to compare Femara (letrozole) for 2.5 years to 5.0 years after the initial five years of any endocrine therapy. Overall a total of 1824 patients were assigned to treatment and after an average follow-up of 6.6 years were compared.
This study failed to demonstrate superiority of 5 years over 2.5 years of extended adjuvant Femara after an initial five years of adjuvant endocrine therapy. A reduction in occurrence of second primary breast cancer was however observed with five years of treatment. Additional clinical trials are ongoing evaluating the optimal duration and type of endocrine therapy and the results of these studies may continue to influence reccomendations.
Reference: Erik J. Blok; Judith R. Kroep; Elma Meershoek-Klein Kranenbarg; Marjolijn Duijm-de Carpentier; Hein Putter; Joan van den Bosch; Eduard Maartense; A. Elise van Leeuwen-Stok; Gerrit-Jan Liefers; Johan W. R. Nortier; Emiel J. Th. Rutgers; Cornelis J. H. van de Velde