Fulvestrant 500 mg Versus Exemestane in Postmenopausal Women With Metastatic Breast Cancer Resistant to Adjuvant Nonsteroidal Aromatase Inhibitors in Clinical Practice: A Multicenter Retrospective Study

Background: Fulvestrant 500 mg and exemestane are widely used agents in first-line therapy for metastatic breast cancer (MBC) of estrogen receptor (ER)-positive (ER⁺) postmenopausal MBC after failure of adjuvant nonsteroidal aromatase inhibitor (NSAI) treatment. Although fulvestrant 250 mg had similar efficacy compared with exemestane (Evaluation of Faslodex versus Exemestane Clinical Trial study) and fulvestrant 500 mg was superior to fulvestrant 250 mg (Comparison of FASLODEX In Recurrent or Metastatic Breast Cancer study), no direct comparison between fulvestrant 500 mg and exemestane has been conducted. The aim of this study was to compare the efficacy and safety of fulvestrant 500 mg and exemestane in daily practice. Patients and Methods: We retrospectively evaluated the medical records of all patients with ER⁺ HER2⁻ MBC who received fulvestrant 500 mg or exemestane 25 mg as first-line therapy for MBC from 2015 to 2017 in 4 institutions. A total of 120 patients were available for analysis. Both agents accounted for 50% (60) patients. Results: The median progression-free survival (PFS) of the fulvestrant group was significantly longer than that in the exemestane group (6.2 months [95% confidence interval (CI), 5.0-7.4] versus 4.8 months [95% CI, 3.0-6.7], P = .024). In subgroup analysis, for patients with visceral metastasis or primary endocrine resistance, no significant difference considering PFS was observed in the 2 groups (P = .563 and .769). No significant difference of Grade 3/4 adverse events was observed in the 2 groups (3 patients, 5% versus 2 patients, 3.3%; P = .648). Conclusion: Fulvestrant 500 mg showed better efficacy than exemestane in first-line therapy for MBC of ER⁺ postmenopausal women after failure of adjuvant NSAI treatment. For patients with visceral metastasis or primary endocrine resistance, both treatments showed poor outcomes, indicating a need for further alternatives (targeted therapy or chemotherapy). Both agents were well tolerated in terms of toxicities. There is no direct comparison of fulvestrant 500 mg and exemestane among metastatic estrogen receptor-positive (ER⁺) breast cancer patients. This retrospective study enrolled 120 patients in China. We found that fulvestrant 500 mg showed better efficacy than exemestane in first-line therapy for metastatic breast cancer of ER⁺ postmenopausal women after adjuvant nonsteroidal aromatase inhibitor treatment failure.