@Jill_Hardin @Eldar @Christian_Reich @Vojtech_Huser One way to potentially surface cancer relapse/recurrence from EHR data is to look for condition_era of a cancer diagnosis followed by a condition era of a history of cancer diagnosis followed by a condition_era of a cancer diagnosis. Z85 and its descendants in ICD10 are supposed to be assigned to patients whose cancer is no longer being treated and no longer exists. See http://www.icd10data.com/ICD10CM/Codes/Z00-Z99/Z77-Z99/Z85-. I agree with @Vojtech_Huser that some kind of referencing between condition_era entries would make explicit relapse/recurrence. Though it might be hard to pull from any source system such explicit linkages. In practice, these linkages are not explicitly recorded in most EMRs. Tumor registries generally do a good job of recording primary site/histology and a not so great job at tracking recurrence. See https://www.ncbi.nlm.nih.gov/pubmed/24504926.