A multicenter study to determine the optimum duration of neoadjuvant letrozole on tumor regression to permit breast-conserving surgery: Final analyses.

670 Background: Neoadjuvant letrozole is currently approved in the UK for the treatment of early breast cancer, to allow breast conserving surgery (BCS) in postmenopausal women with ER-positive breast cancer previously considered suitable for mastectomy only. This approval was based on a study that included 4 months of letrozole treatment. Prospective studies have not investigated treatment duration beyond 6 months and retrospective studies suggest useful responses can occur after this period. The aim of this study was to determine the optimum preoperative duration of treatment with 2.5 mg daily letrozole to permit BCS in patients not suitable for BCS at study entry. Following interim analyses suggesting the percentage of patients who become eligible for BCS increases with duration of letrozole therapy (Carpenter et al., SABCS 2009 [abstract 1082]) we will present final analyses of this 12-month trial. The last patient is scheduled to leave the trial no later than March 2010. Methods: This was a phase 4c ...