This is the CodeSystem that contains all the codes in International Classification of Diseases for Oncology, version 3. (http://terminology.hl7.org/CodeSystem/icd-o-3) and International Classification of Diseases for Oncology, version 3. (http://terminology.hl7.org/CodeSystem/icd-o-3). E.g. what you have to deal with if you get resources containing codes in either of them