A Comparative Study of Exemestane Versus Anastrozole in Patients with Postmenopausal Breast Cancer with Visceral Metastases

PurposePatients developing visceral breast cancer metastases generally receive chemotherapy rather than endocrine therapy. Recent aromatase inhibitor studies have reported activity in such patients; therefore, this study formally evaluated anastrozole and exemestane in postmenopausal patients in this setting.Patients and MethodsPostmenopausal women with advanced breast cancer and ≥ 1 visceral (liver or lung) lesion were randomized to anastrozole (1 mg/day orally) or exemestane (25 mg/day orally) for ≥ 8 weeks. The primary endpoint was objective response in visceral lesions based on modified Response Evaluation Criteria in Solid Tumors. Secondary endpoints included clinical benefit (objective response plus stable disease ≥ 180 days), overall survival, and adverse events.ResultsA total of 130 patients were enrolled, and 128 patients (64 anastrozole, 64 exemestane) were included in the intent-to-treat analysis. Accrual delays caused study closure before the target enrollment (N = 200) was reached, limiting the statistical power of the study. Objective response in visceral sites was approximately 15% in both groups. Clinical benefit in visceral sites was 32% of the patients treated with anastrozole and 38% of the patients treated with exemestane. Median survival was 33.3 months and 30.5 months in the anastrozole and exemestane groups, respectively. Toxicities were similar to those previously reported; however, treatment-related adverse events were more frequent with anastrozole (41%) than with exemestane (31%). Both treatments were generally well tolerated in patients with postmenopausal breast cancer with visceral metastases.ConclusionEfficacy was similar in both treatment groups for all endpoints. Aromatase inhibitors can be considered as a treatment option in postmenopausal patients with hormone receptor–positive visceral breast cancer metastases.