Fulvestrant may extend survival longer than does anastrozole when used as first-line therapy for locally advanced or metastatic estrogen receptor–positive breast cancer, investigators reported online Sept. 14 in the Journal of Clinical Oncology.

Compared with anastrozole, fulvestrant reduced overall mortality risk by approximately 30% in a small international, open-label phase II clinical trial funded by the manufacturer. A double-blind phase III trial is now underway to confirm and extend these preliminary results, said Dr. Matthew J. Ellis of the Lester and Sue Smith Breast Center, Baylor University, Houston, and his associates.

In the phase II study, 102 postmenopausal women were randomly assigned to receive 500 mg fulvestrant and 103 to receive 1 mg anastrozole as first-line therapy at 62 medical centers in 9 countries. Median overall survival was 54.1 months with fulvestrant and 48.4 months with anastrozole, an extension of approximately 6 months (hazard ratio, 0.70). This difference persisted across all subgroup analyses and in a sensitivity analysis, the investigators said (J Clin Oncol. 2015 Sept. 14. doi: 10.1200/JCO.2015.61.5831).

No new safety or tolerability problems occurred. Two serious adverse events that were considered to be treatment related developed in the fulvestrant group: one case of hypertension and one case of pulmonary embolism.

It is relatively uncommon in countries with advanced health care for patients to present with advanced breast cancer that has never been treated with endocrine therapy. Given the high prevalence of the disease, however, this still “represents a numerically substantial patient population” in the West, and it continues to comprise a significant proportion of patients in developing countries, Dr. Ellis and his associates added.

This study was supported by AstraZeneca. Dr. Ellis reported ties to AstraZeneca, Bioclassifier, Pfizer, Novartis, and Celgene; his associates reported ties to numerous industry sources.