Cohort study of physician- and practice-level variation in clinical trial participation among patients with advanced cancer in the United States

Clinical trial enrollment is essential to advancing cancer care, yet participation among patients with advanced cancer remains low. While patient-level barriers are frequently cited, the role of health care delivery factors, specifically physician-and practice-level varation, has been poorly quantified. A cohort study using the Flatiron Health database included 207 743 adult patients with advanced cancers diagnosed and treated betwee 2011 and 2024, by 1664 physicians across 107 trial-available oncology practices. Clinical trial participation was low at 6.8%, with more than 80% of enrollments concentrated among 20% of physicians and practices. Physician- and practice-level factors explained a significantly greater and increasing share or participation variation than patient-level characteristics. The authors conclude that these findings suggest that clinical trial participation in advanced cancer is increasingly driven by structural factors at physician and practice levels, highlighting the need to strengthen physician- and practice-level infrastructure and engagement to enhance equitable access.