Trastuzumab emtansine versus treatment of physician's choice in patients with previously treated HER2-positive metastatic breast cancer (TH3RESA): final overall survival results from a randomised open-label phase 3 trial

Background In the randomised, parallel assignment, open-label, phase 3 TH3RESA study, progression-free survival was significantly longer with trastuzumab emtansine versus treatment of physician's choice in previously treated patients with HER2-positive advanced breast cancer. We report results from the final overall survival analysis of the TH3RESA trial. Methods Eligible patients for the TH3RESA trial were men and women (aged >= 18 years) with centrally confirmed HER2-positive advanced breast cancer previously treated with both trastuzumab and lapatinib (advanced setting) and a taxane (any setting) and with progression on two or more HER2-directed regimens in the advanced setting. Patients had to have an Eastern Cooperative Oncology Group performance status of 0-2, left ventricular ejection fraction of at least 50%, and adequate organ function. Patients were randomly assigned (2: 1) by an interactive voice and web response system with permuted block randomisation in blocks of six to receive trastuzumab emtansine (3.6 mg/kg intravenously every 21 days) or treatment of physician's choice administered per local practice. Randomisation was stratified by world region, number of previous regimens for advanced breast cancer, and presence of visceral disease. On Sept 12, 2012, the study protocol was amended to allow patients with disease progression to crossover from treatment of physician's choice to trastuzumab emtansine. The coprimary endpoints for TH3RESA were investigator-assessed progression-free survival and overall survival in the intention-to-treat population. We report results from a preplanned second interim analysis of overall survival, which was planned for when approximately 67% (n=330) of 492 expected deaths had occurred. This study is registered with ClinicalTrials.gov, number NCT01419197. Findings Between Sept 14, 2011, and Nov 19, 2012, 602 patients were enrolled from 146 centres in 22 countries and randomly assigned to trastuzumab emtansine (n=404) or treatment of physician's choice (n=198). At data cutoff (Feb 13, 2015), 93 (47%) of 198 patients in the physician's choice group had crossed over to trastuzumab emtansine. Overall survival was significantly longer with trastuzumab emtansine versus treatment of physician's choice (median 22.7 months [95% CI 19.4-27.5] vs 15.8 months [13.5-18.7]; hazard ratio 0.68 [95% CI 0.54-0.85]; p=0.0007). As the stopping boundary for overall survival was crossed, this overall survival analysis serves as the final and confirmatory analysis of overall survival and the study was terminated according to the protocol. The incidence of grade 3 or worse adverse events was 161 (40%) of 403 patients in the trastuzumab emtansine group and 87 (47%) of 184 patients in the treatment of physician's choice group. Of the most common grade 3 or worse adverse events (affecting >= 2% of patients in either group), those with a 3% or greater difference in incidence between groups that were more frequent with treatment of physician's choice than with trastuzumab emtansine were diarrhoea (three [1%] of 403 patients in the trastuzumab emtansine group vs eight [4%] of 184 patients in the treatment of physician's choice group), neutropenia (ten [3%] vs 29 [16%]), and febrile neutropenia (one [<1%] vs seven [4%]); whereas those that were more frequent with trastuzumab emtansine were thrombocytopenia (24 [6%] of 403 patients vs five [3%] of 184 patients) and haemorrhage of any type (17 [4%] of 403 vs one [<1%] of 184). Serious adverse events were reported in 102 (25%) of 403 patients in the trastuzumab emtansine group and 41 (22%) of 184 in the physician's choice group. Deaths from adverse events were reported in three patients (2%) in the physician's choice group (of which one was judged to be treatment related) and nine (2%) in the trastuzumab emtansine group (of which three were judged to be treatment related). Interpretation In patients who had progressed on two or more HER2-directed regimens, trastuzumab emtansine treatment resulted in a significant improvement in overall survival versus treatment of physician's choice. These data further solidify the role of trastuzumab emtansine in the management of patients with previously treated HER2-positive advanced breast cancer, and validate HER2 as a therapeutic target even after multiple lines of previous therapy.