Dimension Original Survey Items Promoters:   Physician personal benefits •Local trials keep patients in the community •Frequent contact with PI/researchers •Trial participation gives prestige •Frequent exposure to EPCT information Trial treatment benefits •Possibility of therapeutic benefit to patient •Possibility that experimental treatment is better than standard treatment •Trial provides the best and most current treatment Patient psychosocial benefits •Possibility of psychological benefit to patient •Patient/family wants to try something new •Comfortable explaining EPCTsa •Patients are followed very closelya Logistical barriers:   Clinical trial process burden •Paperwork of referral process is too time-consuming •Too much time required to explain an EPCTs •Excessive details of protocols •No staff support available •Referral procedures are too complex •Referring patients to EPCTs is extra work Coordination/Involvement with clinical trial site •Contacting the PI is too difficult •Contacting the referral office at CT site is too difficult •The institution does not keep me in the loop regarding my patients Personal Barriers: Personal/Attitudes •Don’t want to increase patient’s anxiety •Language barriers with minority patients •Patients will blame the referral oncologist for any adverse effects •Hassle of convincing patients to participate •Difficulty explaining medical uncertainty •Referring patients to trials might negatively affect relationship with patient •Distrust of researchers conducting the trial Lack of personal benefits •Lack of rewards and recognition •Loss of personal income as a result of patients seeking treatment from trial physicians •Fear loss of control over patient care •Lack of awareness about EPCTsa Protocol-Related Barriers: Protocol complexity •Misinterpretation of study protocol •Consent procedure too difficult or complex •Trial protocol too complex •Misinterpretation of eligibility of patients •Eligibility criteria too strict/stringent Trial treatment •Toxicity/side effects of experimental TT outweighs possible benefits •Trial therapy not as good as standard therapy •Low probability of therapeutic benefit to the patient aStand-alone items not related to identified dimensions

Table 2: Dimensions Identified through Exploratory Factor Analysis and Original Survey Items.