International Classification of Diseases for Oncology

The International Classification of Diseases for Oncology (ICD-O) is a domain-specific extension of the International Statistical Classification of Diseases and Related Health Problems for tumor diseases. This classification is widely used by cancer registries.

It is currently in its third revision (ICD-O-3). ICD-10 includes a list of morphology codes. They stem from ICD-O second edition (ICD-O-2) that was valid at the time of publication.

Axes

The classification has two axes: topography and morphology.

Morphology

The morphology axis is for the shape and structure of the tumor.

This axis has particular importance because the Systematized Nomenclature of Medicine ("SNOMED") has adopted the ICD-O classification of morphology. SNOMED has been changing continuously, and several different versions of SNOMED are in use. Accordingly, mapping of ICD-O codes to SNOMED requires careful assessment of whether entities are indeed true matches.

Topography