Prospective evaluation of megestrol acetate after aromatase inhibitor failure in advanced endocrine responsive breast cancer: Preliminary results.

Abstract

1137 Background: There is a recent interest in the evaluation of “old” endocrine treatments in advanced breast cancer. Based on our retrospective data showing median time to treatment failure of 16 weeks with megestrol acetate (MA) after aromatase inhibitor (AI) failure in patients (pts) with endocrine responsive breast cancer, we evaluated the benefit of MA in a prospective setting. Methods: Phase II single- institution study. Eligibility: pts with advanced breast cancer that received AI in the palliative setting for more than 6 months or as adjuvant therapy for more than 12 months and had documented disease progression while on endocrine therapy. Treatment: MA 160 mg/day continuously until disease progression or toxicity. RECIST response evaluation and doppler ultrasound of lower extremities for prospective deep venous thrombosis (DVT) assessment every 8 weeks. Results: Accrual started January 2007 and is still ongoing. As of December 2009, 36 pts entered the trial (out of 46 planned), with 34 pts evaluated for response and toxicity. Median age was 64 years (45-90). Nine pts (25%) had visceral metastasis and 27 (75%) had soft tissue, bone, or pleural disease. Previous treatment included neo/adjuvant tamoxifen in 16 pts (44%), palliative tamoxifen in 17 pts (47%), adjuvant AI in 5 pts (14%), and palliative AI in 31 patients (86%). Median time on palliative AI was 21 months (6-91). One patient had partial response and 11 pts had stable disease for more than 6 months, resulting in a clinical benefit rate of 35%. Median time to progression (TTP) was 16.6 weeks (3-77). Patients with visceral metastasis had median TTP of 12 weeks (7-72) and those without visceral disease 17 weeks (3-77). Treatment was well tolerated and no patient developed grade 3 toxicity or required therapy interruption. Two pts (6%) developed DVT while on MA. Conclusions: This is the first prospective evaluation of MA after AI failure in endocrine responsive breast cancer. Clinical benefit rate and median time to progression are in agreement with approved alternatives in this setting, such as exemestane and fulvestrant (J Clin Oncol 2008;26:1664). Incidence of DVT has been low. Accrual will continue as planned. No significant financial relationships to disclose.