What constitutes reasonable evidence of efficacy and effectiveness to guide oncology treatment decisions?

The need to practice evidence-based medicine is the current prevailing paradigm within the medical community. Evidence to guide practice can and should come from a variety of sources, including clinical trials, observational studies, and meta-analyses of both or either. This paper discusses the relative strengths and weaknesses of data that arise from these various sources. The different types of evidence required to demonstrate "efficacy" versus "effectiveness," a critical and often overlooked distinction, are discussed. In the genomic age, in which targeted therapies with or without specific biomarkers are emerging in cancer care, new approaches are necessary to generate the evidence required for decision making.