• Retrospective analysis of patients previously receiving treatment with single-agent T-DM1.
• 15 of 20 patients who discontinued T-DM1 received further therapy, 12 with anti-HER2 agents, and 5 experienced partial responses.

While there was no particular reason to doubt that patients experiencing disease progression on T-DM1 would respond to further anti-HER2 treatment alone or with chemotherapy, it is reassuring to learn about the 5 patients in this report who did in fact achieve subsequent objective partial responses. From a more macro standpoint, this study further contributes to an extensive tableau of clinical research data supporting the concept of continuing anti-HER2 therapy beyond disease progression and switching out the partner agent(s). The true biology and pharmacology behind this important therapeutic paradigm are far from clear, but the clinical implications have definitely become apparent as most patients with metastatic disease these days receive indefinite HER2 blockade.