Since it was first published in 1976, the International Classification of Diseases for Oncology (ICD-O) has been internationally recognized as the definitive classification of neoplasms. It is used by cancer registries throughout the world to record incidence of malignancy and survival rates, and the data produced are used to inform cancer control, research activity, treatment planning and health economics.

The classification of neoplasms used in ICD-O links closely to the definitions of neoplasms used in the WHO/IARC Classification of Tumours series which are compiled by consensus groups of international experts and, as such, the classification is underpinned by the highest level of scientific evidence and opinion.

ICD-O consists of two axes (or coding systems), which together describe the tumour:

  • the topographical code, which describes the anatomical site of origin (or organ system) of the tumour, and

  • the morphological code, which describes the cell type (or histology) of the tumour, together with the behaviour (malignant or benign).

The third edition of ICD-O (ICD-O-3) has been available in printed format since 2000. In September 2011, following approval by the WHO/IARC Committee for ICD-O-3, the classification was updated with a number of new or modified codes and terms (ICD-O-3 First Revision, or ICD-O-3.1). The printed version of the first revision was published in 20131 and is available from WHO press.

ICD-O-3 online now makes available ICD-O-3 and ICD-O-3.1 as fully searchable electronic resources. The alphabetical index of the printed book has been replaced with an efficient search tool to enable the user to quickly identify specific entities. In addition, the online format has enabled WHO/IARC to enhance the listings with useful definitions of entities from the WHO/IARC Classification of Tumours series and other sources. Further information on the use of ICD-O-3 online can be found here.



1 International Classification of Diseases for Oncology, Third Edition, First Revision. Geneva: World Health Organization, 2013.