While clinical trials offer cancer patients the optimum treatment, historical accrual of such patients has not been very successful. OncoDoc is a decision support system designed to provide best therapeutic recommendations for breast cancer patients. Developed as a browsing tool of a knowledge base structured as a decision tree, OncoDoc allows physicians to control the contextual instantiation of patient characteristics to build the best formal equivalent of an actual patient. Used as a computer-based eligibility screening system, depending on whether instantiated patient parameters are matched against guideline knowledge or available clinical trial protocols, it provides either evidence-based therapeutic options or relevant patient-specific clinical trials. Implemented at the Gustave Roussy Institute and routinely used at the point of care during a 4-month period, it significantly improved physician compliance with guideline recommendations and enhanced physician awareness of open trials while increasing patient enrollment to clinical trials by 50%. But, when analyzing reasons of non-accrual of potentially eligible patients, it appeared that physicians' psychological reluctance to refer patients to clinical trials, measured during the experiment at 25%, may not be resolved by the simple dissemination of clinical trial information at the point of care.