Limitations of clinical trials in sickle cell disease: a case study of the Multi-center Study of Hydroxyurea (MSH) trial and the Stroke Prevention (STOP) trial.

In the past two decades, two landmark randomized controlled trials (RCT) have been completed among individuals with sickle cell disease (SCD), the Multi-center Study of Hydroxyurea (MSH) trial and the Stroke Prevention (STOP) trial. The MSH trial tested the hypothesis that hydroxyurea will reduce the frequency of painful episodes for adults with hemoglobin SS who had a history of 3 or more painful episodes per year. The STOP trial tested the hypothesis that among children with hemoglobin SS and an elevated transcranial Doppler (TCD) velocity measurement, blood transfusion therapy would decrease the risk of an initial stroke. After completion, both trials have defined standard care for individuals with hemoglobin SS. The purpose of this review is to examine the limitations of the MSH and STOP trials. In the context of these trials, we will examine the effects of narrow inclusion criteria that primarily include participants with hemoglobin SS and secondary analyses that are prone to false-positive results. In addition, we describe how after publication of these two trials use of hydroxyurea and TCD assessment has drifted towards a standard practice without evidence of therapeutic efficacy among groups that were excluded from the trials. Finally, we suggest that rigorously conducted RCTs or at the minimum multicenter observation studies with strong methodology should be performed in these excluded subgroups to confirm a benefit of hydroxyurea or TCD measurement.