Cancer Interception Trials Are Hiding in Plain Sight on ClinicalTrials.gov

Cancer prevention has long lived in the shadow of cancer treatment, and a new analysis suggests the world’s largest clinical trial registry is doing little to change that. A cross-sectional study published in Frontiers in Epidemiology examined every prevention and interception-related study registered in ClinicalTrials.gov through September 2025, and found a research landscape that is both vibrant and structurally invisible. Of 296 records initially retrieved, 209 qualified for the final analysis, and their metadata reveal a field that standard registry categories simply were not built to describe.

The scale of the underlying registry is enormous. ClinicalTrials.gov, maintained by the U.S. National Library of Medicine, now hosts more than 345,000 interventional and observational studies and serves as the de facto public record of clinical research activity. But the new analysis, led by Martha Fors of Universidad de Las Américas in Quito, Ecuador, zeroed in on a specific and increasingly important niche: studies designed to stop cancer before it becomes clinically manifest invasive disease. Using search terms spanning chemoprevention, premalignant lesions, precursor conditions, carcinoma in situ, dysplasia, and minimal residual disease, the team assembled a picture of how prevention-oriented science is actually being conducted and, crucially, how it is being labeled.

The concept of cancer interception sits in a biological no-man’s-land between prevention and treatment. Primary prevention targets healthy individuals at risk, aiming to stop the carcinogenic process before it starts. Screening and early detection seek to find existing occult tumors or precursor lesions sooner. Interception, by contrast, intervenes on a measurable biological state, a molecular abnormality, an inherited predisposition, or a histological premalignant lesion, with the goal of halting or reversing progression before invasive cancer develops. A recent framework in Cancer Discovery formalized this spectrum as cancer prophylaxis, interception, and mitigation, but the new study shows that registry infrastructure has not caught up with the science.

The numbers tell a striking story. Of the 209 eligible studies, 157, or 75.1 percent, were interventional and 52 were observational. Just over half, 52.6 percent, had been completed. Among the interventional trials, randomized allocation dominated at 66.9 percent, parallel-group designs accounted for 65 percent, and most studies, 65 percent, were unmasked or open-label. Median estimated enrollment was 150 participants with a wide interquartile range of 61.5 to 533.5, reflecting everything from small biomarker studies to large prevention cohorts. Gynecological and gastrointestinal malignancies led the representation, at 25.4 and 23.4 percent respectively.

That anatomical concentration is not accidental. The authors argue that it reflects a fundamental methodological asymmetry in oncology research. Cervical intraepithelial neoplasia and colorectal adenomas are well-characterized precursor states with identifiable biomarkers, offering feasible endpoints for interception trials within reasonable follow-up periods. For cancers whose earliest biological changes remain elusive or clinically occult, the barrier to designing reproducible interception studies remains high. The registry landscape, in other words, is heavily biased toward what the researchers call high-feasibility biological pathways, potentially leaving unmet needs in less-defined interception domains poorly addressed.

Perhaps the most consequential finding concerns classification. When the team applied an operational framework dividing interventional studies into three categories, primary prevention and chemoprevention, early detection and diagnosis, and cancer interception with post-treatment disease control, the distribution was nearly even: 32.5 percent, 34.4 percent, and 33.1 percent respectively. But only the first two categories have native registry designations, mapping to ClinicalTrials.gov’s Prevention, Screening, and Diagnostic fields. The 52 interception and post-treatment disease-control studies, roughly a third of the interventional portfolio, had no distinct registry home at all, and were scattered across broad categories such as Supportive Care, Basic Science, and Health Services Research.

This structural ambiguity has practical consequences. Interception research often involves populations that are neither healthy individuals in primary prevention nor patients with established cancer, but rather people carrying inherited risk, molecular abnormalities, or precursor lesions. Registry fields that fail to capture these intermediate states obscure the true scope of preventive research, hinder evidence synthesis, and complicate any attempt to quantify global progress in the field. The problem extends to study phase as well: 86 percent of the interventional trials were classified as Not Applicable for phase, because conventional phase I through IV categories were designed for therapeutic drug development and fit poorly with behavioral interventions, devices, nutritional components, and long-term biomarker endpoints.

Funding transparency fared even worse. A staggering 87.6 percent of records, 183 of 209, were classified under the registry’s generic Other funding category, with industry funding at just 6.7 percent and NIH funding at 2.4 percent. Because ClinicalTrials.gov does not disclose the institutional nature of funders coded as Other, the researchers could not determine whether these studies rely on philanthropic capital, academic institutional budgets, or cooperative group support, and any manual attribution would have risked substantial misclassification. A statistically significant association between study type and funding category emerged, p equal to 0.028 with a small Cramér’s V of 0.25, but the authors caution it reflects registry structure rather than a defined investment pattern. Notably, 25.8 percent of studies were restricted to female participants, largely mirroring the gynecological focus.

The team’s proposed remedies are concrete. They call for a dedicated Prevention/Interception Stage classification distinguishing primary prevention, biological interception, and post-treatment control; mandatory disaggregation of funding sources into philanthropic, academic institutional, cooperative group, and industry categories; a structured metadata field for baseline biological or risk status capturing genetic, molecular, or histopathological markers; and standardized tagging of primary trial objective to cleanly separate early detection from progression interruption. Such refinements, they argue, would improve visibility, traceability, and cross-trial comparability in preventive oncology.

The study carries its own caveats, which the authors are careful to spell out. Restricting the analysis to ClinicalTrials.gov introduces geographic and structural bias toward North American research networks, and trials registered exclusively in the EU Clinical Trials Information System, the Japan Registry of Clinical Trials, or the WHO ICTRP network were not captured. Whether adopting prevention-specific metadata fields would actually accelerate clinical translation of interception research remains a hypothesis for future evaluation. Still, the message lands with force: cancer interception has matured into a distinct clinical discipline, and the registries that index human research have not yet learned to see it. Until they do, a third of the field’s clinical trials will remain scattered across categories that describe everything except what these studies are actually trying to do.

Subject of Research: Registry-based landscape analysis of cancer prevention and interception trials on ClinicalTrials.gov

Article Title: Cancer prevention and interception studies registered in ClinicalTrials.gov: a landscape analysis of trial characteristics and reporting gaps

Article References: Fors, M., González, P., Torres, A., Silva-Guayasamín, L., & Silva-Sarabia, C. (2026). Cancer prevention and interception studies registered in ClinicalTrials.gov: a landscape analysis of trial characteristics and reporting gaps. Frontiers in Epidemiology, 6, Article 1943268. https://doi.org/10.3389/fepid.2026.1943268

Image Credits: AI Generated

DOI: 10.3389/fepid.2026.1943268

Keywords: cancer interception, cancer prevention, chemoprevention, ClinicalTrials.gov, clinical trial registries, premalignant lesions, minimal residual disease, preventive oncology, trial metadata, funding transparency, early detection, epidemiology