These findings led to interest in the medical community whether adult emphysema patients might get symptomatic relief from treatment with all-trans-retinoic acid. In September 1998, the NHLBI convened a workshop, entitled "Clinical Trial Feasibility: All-trans-Retinoic Acid for the Treatment of Emphysema", to discuss the feasibility of a clinical trial to test the efficacy of retinoic acid in the treatment of emphysema. The workshop participants agreed that the laboratory findings were exciting, but that a proof of principle study was needed to demonstrate whether the laboratory findings could be applied to humans with emphysema. Since there was adequate information about the dose range and toxicity of retinoids in humans, adequate methods for assessing the extent of emphysema, and adequate methods to assess the biological activity and distribution of retinoids in the human lung, the workshop participants thought studies in emphysema patients were possible and appropriate. Several possible populations and retinoids, especially the retinoic acids, were discussed as appropriate for a clinical trial. However, the participants did not think that there was sufficient information available to recommend a single trial design and recommended the conduct of multiple small trials, allowing flexibility in the choice of population, retinoid, doses, and outcomes.