Clinical Trial Components of NIH Career Development Awards: Supporting the Nation's Future Trialists.

In 2027, the National Institutes of Health (NIH) will no longer support costs associated with clinical trials (CT) for career development (K) awards. NIH's CT definition encompasses many types of research, from early-stage pilot work through definitive studies. The types and sizes of trials K awardees conduct have not been described, which could inform ongoing policy changes relevant to the next generation of clinical trialists. We conducted a cross-sectional analysis of NIH RePORTER data to characterize the types and sizes of CTs supported by NIH K01, K08, and K23 awards funded in fiscal years 2024-2025 under a CT Required or CT Optional funding opportunity announcement (FOA), with non-missing abstract text. A rule-based classification scheme applied to free-text abstracts categorized each award into 5 mutually exclusive trial types: pilot/feasibility/proof-of-concept, efficacy/effectiveness, trial confirmed with type unclear, other (mechanistic, ancillary, or phase I/II), or no trial-specific language identified. Trial size was assessed among abstracts reporting an explicit, manually verified sample size. Of 1336 unique awards funded under CT Required (n=1051) or CT Optional (n=285) FOAs, 815 (61.0%) were classified as pilot, feasibility, or proof-of-concept studies, and 55 (4.1%) as efficacy or effectiveness studies; 204 (15.3%) had a confirmed trial of unclear type, 41 (3.1%) were other, and 221 (16.5%) had no trial-specific language. Among CT Required awards, 730 (69.5%) were pilot, feasibility, or proof-of-concept work. Among 273 awards (20.4%) with a verified sample size, the median was 60 participants (IQR, 44-80), with 236 (86.4%) enrolling ≤100 participants. Given these findings that CT within NIH K awards are generally small and early-stage, NIH's decision to no longer support trial costs may adversely affect the scientist development pipeline.