Background: The randomized, controlled trial (RCT) is the "gold standard" for establishing the effect of any intervention. This approach, however, is often not feasible with rare diseases such as cutaneous T-cell lymphoma.
Methods: We review the principles of evidence-based medicine to see which are particularly pertinent to the study of rare diseases.
Results: When an RCT is not feasible, attention is given to determining all the available prior data. Evaluation of the new data and the historic base requires attention to biases, but can allow estimation of a "true" study result.
Conclusions: Even when an RCT cannot be performed because of insufficient cases, utilization of evidence-based methodology can help minimize bias and maximize the truth of observed new data.