Overview of NCI Thesaurus (NCIt)
NCI Thesaurus (NCIt) (download) is NCI's reference terminology and ontology. NCIt provides responsive, science-based terminology concepts used in NCI semantic infrastructure and information systems. It covers terminology for clinical care, translational and basic research, and public information and administrative activities. NCIt is also a widely recognized standard for biomedical coding and reference, used by a broad variety of public and private partners both nationally and internationally.
NCIt content comes from NCI, NIH, agencies and standards development organizations such as FDA and CDISC, other partners, user requests, and ongoing review of the scientific literature (see EVS Use and Collaborations). This content is organized in a richly structured description logic environment, with more than 900,000 relationships between concepts to help define and connect them. Individual concepts include codes, terms, abbreviations, synonyms, definitions, links to outside sources, and a wide variety of other useful information.
More complete description of the semantics of NCIt is available. A document briefly describing the editorial policies governing change to NCIt content is included with the semantics information.
The NCI Thesaurus is updated monthly, averaging roughly 700 new concepts and many additional changes with each release. Complete change history for each concept is provided through EVS APIs and browsers.
NCIt is registered in the HL7 OID Registry 
as 2.16.840.1.113883.3.26.1.1 .
NCIt provides cross-links and semantics for a broader range of EVS terminology resources. NCIt is the lead reference for the NCI Metathesaurus (NCIm), which provides rich synonymy and mappings among the codes and terms used in more than 100 biomedical terminologies. EVS cross-links NCIt and NCIm to a wide variety of other terminologies and ontologies that are published separately, such as CTCAE, GO, ICD-10-CM, LOINC, MedDRA, SNOMED CT, and the VA's MED-RT.
