Racial and Ethnic Reporting and Representation in Phase III Alzheimer's Disease Clinical Trials in the US.

Background: Alzheimer's disease (AD) disproportionately affects racial and ethnic minoritized populations in the United States, yet these groups remain markedly underrepresented in clinical research. Phase III clinical trials are critical for informing regulatory decision and treatment guidelines, but the extent to which they report and include racial and ethnic diverse participants in the US context has not been systematically assessed. Methods: We conducted a comprehensive retrospective review of all US-based Phase III AD clinical trials from 1997 to 2023 using the Trialtrove database, cross-referenced with PubMed, ClinicalTrials.gov, and other public sources. We analyzed long-term trends in the reporting and representation of racial and ethnic groups across the longest observation period to date. Results: Of 88 identified trials, 71 (80.7%) had published data. Nearly half (49.3%) did not report any race or ethnicity information. Among those that did, most focused on White patients, with limited and inconsistent reporting for racial and ethnic minoritized groups. Median enrollment was 0.9% for Asian or Pacific Islander, 4.5% for Black (ethnicity unspecified), 7.2% for Black (non-Hispanic), 5.2% for Hispanic, and 0.4% for Native American participants, compared to nearly 90% for White participants. Only 4.2% of trials conducted subgroup analysis by race or ethnicity, and none reported detailed outcome differences. Terminology varied widely and no trials acknowledged underrepresentation or proposed corrective strategies. Notably, these patterns showed little to no improvement over time. Conclusions and Implications: Racial and ethnic minoritized populations remain consistently underreported and underrepresented in Phase III AD trials in the US, limiting the generalizability of findings and risking the exacerbation of health inequities. Improving equity in AD research will require standardized reporting, inclusive recruitment practices, and intentional efforts to engage underrepresented communities.