Background: The non-steroidal reversible aromatase inhibitor (AI), anastrozole (A) is approved as adjuvant monotherapy in hormone receptor (HR) positive early breast cancer (EBC). The steroidal irreversible AI exemestane (E) is approved in sequence after an initial 2-3 years of tamoxifen. MA27 tested the hypothesis that exemestane would have greater efficacy and better end-organ safety than anastrozole for several reasons: E is an irreversible and more potent AI than A; unlike A, E does not induce intra-tumoral aromatase and; through its mild androgenic activity E may exert a second anti-tumor effect and a more favorable bone and lipid metabolism profile than A. Initially the study also tested the role of a cyclooxygenase-2 inhibitor, celecoxib, used in combination with an AI. However, celecoxib was discontinued early in MA27 following identification of cardiovascular toxicity with COX-2 inhibitors. Methods: Postmenopausal women with hormone receptor positive primary breast cancer were randomized after adequate local treatment to 5 years of adjuvant A (1mg/day) or E (25mg/day) with or without celecoxib/placebo (400mg/plac twice daily for 3 years). The primary objective is the comparison of event free survival (EFS) between women treated with A or E. Secondary objectives include overall survival (OS), distant recurrence (DDFS), incidence of contralateral breast cancer (CBC) and safety. Quality of Life in a subset of women has been evaluated, and a very extensive tissue bank created. Stratification included: prior chemotherapy; lymph node status, celecoxib (during use), aspirin use (during randomization to celecoxib), and trastuzumab use (since November 2005). The primary endpoint (EFS) will look for an improvement from 87.5% to 89.9%; HR 0.80, 2-sided 5% level and 80% power, with 644 events required. Results: 7576 women were randomized between June 2003 and July 2008. Celecoxib/placebo, was discontinued 2 years into the trial in December 2004 after 1635 patients had received celecoxib. The number of events required for final analysis was reached April 2010. Patient characteristics were balanced for age (median 64.1yrs); race; ECOG PS; mastectomy; TNM staging and; prior adjuvant chemotherapy. EFS, OS, DDFS, and CBC as well as clinical fractures, cardiovascular events and adverse events will be presented by arm in the final analysis.

Conclusions: NCIC CTG MA.27 is the first definitive EBC trial comparing a non-steroidal and steroidal AI as initial adjuvant therapy. Exemestane is not currently approved as initial adjuvant treatment and superiority or equivalence will lead to its inclusion as a first-line option for EBC in postmenopausal HR positive breast cancer. Efficacy, clinical fractures, cardiovascular events and AI related symptoms will help to define the cost-benefit ratios of these two AIs.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S1-1.