A phase III trial of exemestane plus bevacizumab maintenance therapy in patients with metastatic breast cancer after first-line taxane and bevacizumab: a GINECO group study

Background: Maintenance strategies beyond response or tumor stabilization with first-line chemotherapy in metastatic breast cancer (MBC) have not been extensively studied. Endocrine therapy combined with continued bevacizumab may be a helpful option for estrogen receptor (ER)-positive MBC.

Patients and methods: In this prospective, open-label, phase III study, patients with histologically confirmed ER-positive, HER2-negative MBC and non-progressive disease after 16-24 weeks of taxane plus bevacizumab (T + BEV) were randomized to continuation of T + BEV or maintenance bevacizumab plus exemestane (E + BEV). The primary end point was progression-free survival (PFS) from randomization. To have 80% power to detect an improvement in the 6-month PFS rate (PFS6m) from 50% to 65%, 186 assessable patients were needed for a total of 141 PFS events. An interim analysis was planned after 40% of the required events.

Results: The interim analysis with 98 patients showed that the probability of reaching a statistically significant improvement in PFS by the end of the study was only 7%. This led the Independent Data and Monitoring Committee to recommend termination of patient enrollment. After a median of 21-month follow-up of all randomized patients (117 in total), PFS6m from randomization was 67.2% [95% confidence interval (CI) 53.6-77.7] with T + BEV and 55.2% (95% CI 41.5-66.9) with E + BEV [hazard ratio (HR): 1.0, 95% CI 0.7-1.5, P = 0.998]. Median PFS from BEV initiation was 12.5 and 12.3 months in the T + BEV and E + BEV arms, respectively. In the T + BEV arm, taxane was prematurely stopped for the majority of patients (94.9%), mainly due to toxicity (49.2%). Updated data after 35 months' median follow-up showed death rates of 44% and 55% in T + BEV and E + BEV arms, respectively.

Conclusion: In this trial, maintenance therapy with E + BEV in ER-positive, HER2-negative MBC patients with no evidence of progression after first-line T + BEV did not achieve longer PFS compared with continuation of T + BEV.

Clinicaltrialsgov: NCT01303679.