Standardization of immunotherapy adverse events in patient information leaflets and development of an interface terminology for outpatients' monitoring.

•Standardized symptom terms enable patients to report reusable drug adverse event data.•Patient Information Leaflets contain significant information in free text.•Patient Information Leaflets mix patient-reportable and doctor-reportable events.•A workflow for the standardization of the package information leaflets is proposed.•The resulting interface terminology forms a basis for a mobile application for ePROs.