ImportanceClinical trials are critical for progress in oncology; however, only 5% of the adult cancer population participates. Harnessing data that are routinely collected (ie, electronic patient-reported outcomes [ePROs]) may serve as a method to promote trial enrollment.ObjectiveTo evaluate if an ePRO-prompted recruitment strategy is associated with increased clinical trial enrollment.Design, Setting, and ParticipantsA randomized substudy was conducted from September 2022 to March 2023 at a multisite tertiary cancer center as part of an ongoing clinical trial that was testing a symptom-intervention for cancer-related fatigue. Patients with breast cancer who were undergoing radiotherapy who completed at least 1 ePRO questionnaire during the study period were included. Physician-level cluster randomization assigned fatigue-eligible patients to either receive a portal message invitation to a symptom-intervention trial or standard of care (SOC; physician-based referral).ExposureePRO questionnaires distributed in routine practice were queried weekly and screened for moderate or greater fatigue, the principle inclusion criterion for the primary trial. To assess the association of the portal message source with response and enrollment, every other patient received a message from the primary radiation oncology team or the referral service.Main Outcomes and MeasuresClinical trial response/referral and enrollment.ResultsA total of 1041 patients completed ePRO questionnaires, of whom 394 (38%; 53 Asian [13.6%], 43 Black [11.0%], 29 Hispanic [7.4%], and 262 White individuals [66.5%]; median [IQR] age, 55 [47-65] years) endorsed moderate or greater fatigue while receiving treatment. A total of 210 patients (53.3%) were assigned to receive a portal message and 184 (46.7%) patients, SOC. In the portal message group, 73 patients (35%) responded and 41 (20%) enrolled compared with 1 patient (0.5%) referred and 0 enrolled in the SOC group (P < .001). The response rate to portal messages favored the referral service vs the primary radiation oncology service (44% vs 26%; P = .01), but there was no significant difference in enrollments.Conclusions and RelevanceThe study results suggest that use of routine care ePROs was associated with greater enrollment in a symptom-intervention trial compared with physician-based referral. Messaging directly from the referral service may support enrollment and help reduce oncology physician-level barriers to trial enrollment for studies testing symptom interventions.