Changing the trajectory of Alzheimer’s disease: What is a meaningful delay in disease progression?

Abstract

AbstractBackgroundRecent trials of anti‐amyloid therapies have shown it is possible to change the course of early symptomatic Alzheimer’s disease (AD). However, the limited durations of these trials with the associated limited decline in the patient populations have left questions about the clinical meaningfulness of the observed treatment differences. Through progression analysis, one can quantify trial results in terms of time delay of progression. Compared to treatment differences on clinical scales, time delays are arguably more interpretable to patients and their families. However, it is yet to be established what constitutes a meaningful time delay in AD progression.MethodAssess how different hypothetical delays in disease progression in early symptomatic AD translate into treatment differences on the Clinical Dementia Rating Sum of Boxes (CDR‐SB) based on published results placebo‐arm trajectories in recent anti‐amyloid trials. Estimates are compared to published estimates of minimal clinically important differences (MCIDs) in AD and meaningful delays in progression in other diseases.ResultBased on placebo arms from six recent trials of anti‐amyloid antibodies, a 6‐month delay over 18 months (33% slowing) corresponded to treatment differences on CDR‐SB between ‐0.5 and ‐0.8, a 12‐month delay (67% slowing) corresponded to treatment differences between ‐1.0 and ‐1.7, and completely stopping progression (18‐month delay) corresponded to treatment differences between ‐1.6 and ‐2.3 (Figure 1, Table 1). Observed treatment effects in the EMERGE, CLARITY‐AD and TRAILBLAZER‐ALZ trials are consistent with approximately 4‐6 months delay of progression (22‐30% slowing, Figure 1). Established MCIDs in CDR‐SB in early AD range between 1.0 and 1.6, suggesting that a 12‐month delay or 67% slowing of disease progression in an 18‐month trial would be considered borderline in terms of clinical meaningfulness.ConclusionQuantifying treatment effects in progressive diseases such as AD in terms of time delays or slowing of progression may offer a more meaningful interpretation of the treatment effects. Based on the trajectories of placebo group in recent trials, we found that treatment effects matching conventionally used MCIDs in AD would correspond to a very substantial slowing of disease (>67%), suggesting that current MCIDs for CDR‐SB are likely inflated.