ICD-O and ICD

Relationship

The ICD-O topography axis uses the ICD classification of malignant neoplasms (except those categories which relate to secondary neoplasms and to specified morphological types of tumors) for all types of tumors, thereby providing greater site detail for non-malignant tumors than is provided in ICD. In contrast to ICD, the ICD-O includes topography for sites of hematopoietic and reticuloendothelial tumors.

The topography codes in ICD-O-3 are based on the codes in Chapter II of ICD-10. See the ICD-10-CM module for information about the Clinical Modification of ICD-10.

Similarities

All ICD-O-3 topography codes are four characters in length and begin with the letter C. This is because the topography codes are based on the ‘C” codes in Chapter II of ICD-10.

Differences

There are basic differences between the structure of the ICD and ICD-O. ICD Chapter II (Neoplasms) contains the codes for most benign and all malignant neoplasms. Certain benign neoplasms may be found in the specific body systems chapters. To properly code a neoplasm using ICD, it is necessary to determine from the record if the neoplasm is benign, in situ, malignant or of uncertain histologic behavior. If malignant, any secondary (metastatic) sites should also be determined.

In contrast, ICD-O uses only one set of four characters for topography (based on the malignant neoplasm section of ICD). For example, the topography code (C34._, lung) remains the same for all neoplasms of that site:

The behavior code is incorporated as the fifth digit in the morphology field. The behavior code identifies whether the neoplasm is benign, in situ, malignant, of uncertain histologic behavior, or metastatic.

Updated: December 13, 2023