The use of biomarkers to "personalize" cancer treatment--identifying discrete genes, proteins, or other indicators that can differentiate one type of cancer from another and enable the use of highly tailored therapies--offers tremendous potential for improved outcomes and lower treatment costs. However, the rapid development of cancer biomarker, or genomic, tests--combined with a paucity of evidence to support the effectiveness of the tests--presents a challenge for patients, clinicians, and other stakeholders. In this article we propose that comparative effectiveness research be used to strengthen what is now a haphazard process for developing and marketing cancer biomarker tests. We suggest novel funding approaches and a systematic process for moving from regulatory approval to the generation of evidence that meets the needs of stakeholders and, ultimately, patients.