Whether to continue trastuzumab after objective evidence of disease progression or not is an important unanswered clinical question for women with metastatic disease. This question is also relevant for those who relapse after adjuvant trastuzumab-containing therapy. Unfortunately, there is little evidence to guide decision-making. The modest toxicity and the possible, but unproven, benefit from the continued use of trastuzumab may account for the currently wide spread practice of continued administration of this drug after progression. However, there is no convincing evidence to support the use of extended trastuzumab therapy after progression. At least two randomized trials with no trastuzumab in the control arms were attempted but failed to accrue patients. In the absence of results from a randomized clinical trial, a central registry program that collects information longitudinally from a large number of patients with HER-2 positive breast cancer during the course of their disease was initiated (RegistHER, www.registher.com) to learn about the long term side effects and benefits of prolonged trastuzumab therapy. The anticipated introduction of second generation HER2-targeted agents into the clinic also raises a new question; will switching to these agents be more effective than continuation of trastuzumab? Clinical trials are currently planned to address question prospectively.