Safety of everolimus plus exemestane in patients with hormone-receptor-positive, HER2-negative locally advanced or metastatic breast cancer progressing on prior non-steroidal aromatase inhibitors: Primary results of a phase IIIb, open-label, single-arm, expanded-access multicenter trial (BALLET)

Background: This European phase IIIb, expanded-access multicenter trial evaluated the safety of EVE plus EXE in a patient population similar to BOLERO-2. Patients and methods: Post-menopausal women aged ≥18 years with hormone receptor-positive, human epidermal growth factor-receptor-2-negative advanced breast cancer (ABC) recurring/progressing during/after prior non-steroidal aromatase inhibitors were enrolled. The primary objective was safety of EVE plus EXE based on frequency of adverse events (AEs), and serious AEs (SAEs). The secondary objective was to evaluate AEs of grade 3/4 severity. Results: The median treatment duration was 5.1 months [95% confidence interval (CI) 4.8-5.6] for EVE and 5.3 months (95% CI 4.8-5.6) for EXE. Overall, 2131 patients were included in the analysis; 81.8% of patients experienced EVE- or EXE-related or EVE/EXE-related AEs (investigator assessed); 27.2% were of grade 3/4 severity. The most frequently reported non-hematologic AEs were (overall %, % EVE-related) stomatitis (52.8%; 50.8%) and asthenia (22.8%; 14.6%). The most frequently reported hematologic AEs were (overall %, % EVE-related) anemia (14.4%; 8.1%) and thrombocytopenia (5.9%; 4.6%). AE-related treatment discontinuations were higher in elderly (≥70 years) versus non-elderly patients (23.8% versus 13.0%). The incidence of EVE-related AEs in both elderly and non-elderly patients appeared to be lower in first-line ABC versus later lines. The incidence of AEs (including stomatitis/pneumonitis) was independent of BMI status (post hoc analysis). Overall, 8.5% of patients experienced at least one EVE-related SAE. Of the 121 on-treatment deaths (5.7%), 66 (3.1%) deaths were due to disease progression and 46 (2.2%) due to AEs; 4 deaths were suspected to be EVE-related. Conclusions: This is the largest ever reported safety dataset on a general patient population presenting ABC treated with EVE plus EXE and included a sizeable elderly subset. Although the patients were more heavily pretreated, the safety profile of EVE plus EXE in BALLET was consistent with BOLERO-2. Clinical trial registration: EudraCT Number: 2012-000073-23.