Patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer benefit from an estimated 7 additional months of survival if treated with trastuzumab emtansine rather than the physician’s choice of therapy, according to research published in The Lancet Oncology [published online May 16, 2017; doi:10.1016/S1470-2045(17)30313-3].
A previous phase III trial showed a progression-free survival benefit among patients with previously treated, HER2-positive advanced breast cancer when treated with the antibody-drug conjugate trastuzumab emtansine rather than the physician’s choice of therapy. However, data regarding overall survival (OS) outcomes from the same study had yet to be determined.
Ian E Krop, MD, Dana-Farber Cancer Institute, Harvard Medical School (Boston, MA), and colleagues published the concluding OS data from the study. Among the 972 patients with HER2-positive breast cancer deemed eligible for the study, 602 were randomly assigned (2:1) to receive either trastuzumab emtansine (n = 404) or physician’s choice of therapy (n = 198). The median number of previous treatments for disease in both groups was 4.
Researchers allowed crossover between treatment arms. Approximately half of the patients in the physician’s choice arm crossed over to the trastuzumab emtansine arms by the data cutoff.
Despite the large percentage of crossover, median OS in the trastuzumab emtansine arm was 22.7 months, compared with 15.8 months in the physician’s choice arm. The difference in OS favored the patients treated with trastuzumab emtansine by nearly 7 months.
Grade 3 adverse events were reported among both arms. Forty percent of patients in the trastuzumab emtansine arm exhibited a grade 3 or worse adverse event, leading to 3 treatment-related deaths. Similarly, 47% of patients in the physician’s choice arm exhibited a grade 3 or worse adverse event, amounting to 1 treatment-related death.
Authors of the study concluded that these results have “profound implications for drug development in HER2-positive metastatic breast cancer, suggesting that other drugs targeting HER2 might provide patients with additional clinical benefit.”—Zachary Bessette