First-line endocrine therapy for postmenopausal patients with hormone receptor-positive, HER2-negative metastatic breast cancer: a systematic review and meta-analysis

Background In establishing the 2018 Breast Cancer Practice Guidelines of the Japan Breast Cancer Society, we explored the optimal first-line endocrine therapy for advanced postmenopausal hormone receptor-positive breast cancer. Methods We performed a systematic review of relevant reports from randomized-controlled studies published prior to November 2016 found using medical journal search engines. The main outcomes which we evaluated were progression-free survival (PFS), objective response rate (ORR), disease control rate (CBR), and toxicity. Results Four controlled trials comparing aromatase inhibitors (AI) and cyclin-dependent kinase (CDK)4/6 inhibitor combination therapy to AI monotherapy, and two controlled trials comparing anastrozole to fulvestrant 500 mg were analyzed. AI/CDK4/6 inhibitor combination therapy significantly improved PFS (Risk Ratio: 0.67, 95%CI 0.60-0.73), increased ORR (Risk Difference: 0.11, 95% CI 0.07-0.16), and increased CBR (Risk Difference: 0.11, 95% CI 0.07-0.15), compared with AI monotherapy. Patients who received this combination therapy had a higher grade >= 3 adverse event rate more than those who received AI monotherapy (Risk Difference: 43%, 95%CI: 0.39-0.47). Fulvestrant 500 mg alone significantly improved PFS (risk ratio: 0.85, 95%CI 0.72-0.98), but ORR and CBR were similar to those of anastrozole alone. Conclusion In the first-line treatment for advanced postmenopausal hormone receptor-positive breast cancer, a combination therapy of CDK4/6 inhibitors and AI showed significant improvement of PFS, ORR, and CBR but with significant increased toxicities compared with AI alone. Fulvestrant 500 mg monotherapy significantly prolonged PFS compared with AI monotherapy. We must wait for the results of the studies with longer follow-up period.