Interim analysis in clinical trials: caution against premature conclusions—the SWOG multiple myeloma S0777 case study

BACKGROUND: Interim monitoring for efficacy and futility provides critical decision-making boundaries on early termination of randomized clinical trials. Such analyses can accelerate access to effective therapies and limit exposure to ineffective ones, but this must be weighed against premature closure that can risk obscuring a true treatment benefit. We discuss these considerations and present a case study highlighting the importance of following a well-designed interim analysis plan. METHODS AND FINDINGS: SWOG Cancer Research Network (SWOG) S0777 was a randomized phase III study of bortezomib, lenalidomide, and dexamethasone (VRd) versus Rd in newly diagnosed multiple myeloma that incorporated two pre-planned interim analyses. At both interim analyses, while the futility stopping boundaries were not crossed, the accumulating data suggested a limited or diminishing benefit in progression-free survival (PFS). In contrast, at final analysis, VRd demonstrated significant improvement in both PFS (hazard ratio (HR) = 0.71, p = 0.0018) and overall survival (HR = 0.71, p = 0.025) compared to Rd, helping establish VRd as standard of care. Retrospective analysis shows that use of common alternative futility stopping rules would have also not been crossed, despite the lack of positive results at the interim analysis. CONCLUSIONS: S0777's success underscores the importance of pre-specified interim monitoring plans and cautions against premature trial termination.