Efficacy and toxicity of extended aromatase inhibitors after adjuvant aromatase inhibitors-containing therapy for hormone-receptor-positive breast cancer: a literature-based meta-analysis of randomized trials

Background Endocrine therapy with aromatase inhibitors (AIs) is the cornerstone of adjuvant systemic treatment for postmenopausal patients with hormone receptor-positive breast cancer. It has become clear that hormone receptor-positive breast cancer carries a consistent risk of relapse up to 15 years after diagnosis. Extended duration of adjuvant AIs therapy after completing initial standard adjuvant AIs-containing therapy may prevent late recurrence and death. We performed a meta-analysis to assess the real impact of the extended adjuvant therapy with AIs. Methods A literature-based meta-analysis of the randomized controlled trials (RCTs) was undertaken. Relevant publications from PubMed, Embase, Cochrane Library, and abstracts from American Society of Clinical Oncology (ASCO) and San Antonio Breast Cancer (SABCS) symposia were searched. The endpoints were disease-free survival (DFS), overall survival (OS), local recurrence, distant recurrence, contralateral breast cancer, non-breast cancer-related death, and toxicity. Results Eight trials comprising 15,966 patients met the inclusion criteria. The pooled analysis revealed a significant improvement in DFS (RR = 0.79; 95% CI 0.68–0.91), distant recurrence (RR = 0.75; 95% CI 0.58–0.96), and contralateral breast cancer (RR = 0.53; 95% CI 0.40–0.70) in the extended AIs group. While there was not significant improvement in OS (RR = 1.00, 95% CI 0.99–1.01), non-breast cancer-related death (RR = 1.16, 95% CI 0.96–1.41), and local recurrence (RR = 0.82; 95% CI 0.64–1.06), the subgroup analysis showed that the patient with tumor size > 2 cm (HR = 0.74, RD = − 0.31, P = 0.05 vs. HR = 0.85, RD = − 0.16, P = 0.20), node positive status (HR = 0.77, RD = − 0.27, P =