1556 Background: Access to cancer clinical trials varies geographically in the U.S., yet the relationship between trial availability and population-level cancer outcomes is poorly characterized. Understanding this relationship is critical for policymakers and trial sponsors seeking to reduce disparities in cancer outcomes. Methods: We conducted an ecological analysis of U.S.-based cancer treatment trials (1990–2025). Trial availability was measured using population-adjusted cumulative trial density (trials/10,000 population) and classified as none, low, medium, or high. County-level cancer mortality-to-incidence ratios (MIRs) were used to indicate post-diagnosis outcomes (lower MIR is better). Associations with trial density were assessed using logistic regression, with and without adjustment for the structural factors, including area deprivation index (ADI), health system performance, and area type (metro, micro, non-metro/non-core). Analyses were stratified by area type and ADI to stabilize estimates and assess associations across strata. Results: Between 1990 and 2025, 32,332 U.S.-based trials were conducted. The majority of counties (1,680, 52%; 10% of the U.S. population) had no trials. In counties with trials, counts ranged from 1 to 6,840 and density from 0.05 to 1,992 per 10,000 population. Compared to counties without trials, low-, medium-, and high-density counties were more likely to have lower MIR (OR = 1.9, 3.6, and 3.3, respectively; all p < .001). After adjustment for structural factors, associations persisted in medium- and high-density counties (OR = 1.7, 1.9; p < .001), but not in low-density counties (OR = 1.2; p = .30). Associations were strongest in metro counties (Table), with ORs of 1.91, 2.61, and 2.61 in high-ADI areas (all p<0.0001). In low-ADI areas, medium and high density were associated with lower MIR (OR=2.58 and 2.00; p<.001), but low density was not (OR=1.33; p=0.70). Conclusions: Cancer clinical trial availability in the U.S. is highly concentrated and strongly associated with improved population-level cancer outcomes. The co-occurrence of low trial density, structural deprivation, and higher cancer MIRs highlights opportunities to improve cancer outcomes by expanding the geographic reach of trial infrastructure. Associations between trial density and MIR. Areas Trial Density OR* p Adjusted OR* p All counties None Ref Low 1.90 <.001 1.16 .30 Medium 3.64 <.001 1.72 <.001 High 3.34 <.001 1.86 <.001 Metro None Ref Low 2.10 .005 1.37 .30 Medium 3.70 <.001 2.31 .005 High 4.13 <.001 2.83 .001 Micro None Ref Low 1.35 .05 1.10 .60 Medium 2.00 .001 1.33 .20
Xiao et al. (Wed,) studied this question.