A new biosimilar to trastuzumab (Herceptin) has proven effective in treating women without prior treatment for ERBB2 (HER2)-positive metastatic breast cancer. Trastuzumab is a biologic, a drug comprised of large, complex molecules derived from living organisms. Biosimilars have to demonstrate they are “highly similar” to the reference biologic product, but head-to-head studies are not required for approval. In this case, researchers performed a head-to-head study to compare the proposed trastuzumab biosimilar along with taxane to trastuzumab plus taxane in a 1:1 double-blind, randomized, parallel-group, Phase III equivalency study in 458 treatment-naïve women presenting with ERBB2-positive metastatic breast cancer. The overall response rate at 24 weeks was 69.6% for the biosimilar-based treatment vs. 64.0% for trastuzumab (overall response rate ratio, 1.09; 90% confidence interval, 0.974-1.211). At week 48, there was no statistical difference for time-to-tumor progression, progression-free survival, or overall survival. Adverse events were similar. The authors concluded that use of a proposed trastuzumab biosimilar compared with trastuzumab resulted in an equivalent overall response rate at 24 weeks (JAMA 2017;317:37-47). Two separate editorials lauded the findings of this study and suggested biosimilars may increase access to treatment for cancer patients worldwide.