This is the CodeSystem that contains all the codes in NCI Thesaurus (http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl) and NCI Thesaurus (http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl). E.g. what you have to deal with if you get resources containing codes in either of them