Basic information on ICD-O-3

The ICD-O-3 is a dual classification and coding system for both topography and morphology of a neoplasm. The topography code uses the same three- and four-character categories as ICD-10 for malignant neoplasms (C00-C80), allowing greater specificity for the site of nonmalignant neoplasms than is possible in ICD-10. The morphology code describes the specific histologic cell type and its behaviour. It indicates the specific histologic term.

ICD-O-3 consists of six main sections:

• Introduction
  It describes the historical background of the ICD-O-3, some differences to the ICD-10 and gives some basic information on the structure of the ICD-O-3.
• Instructions for Use
  It includes instructions for use and rules for implementation in tumor (cancer) registries and pathology laboratories and gives some examples of coding.
• Topography - Numerical List
  The topography section has been adapted from the malignant neoplasm section of Chapter II of ICD-10. These topography terms have four-character codes that run from C00.0 to C80.9. A decimal point (.) separates subdivisions of the three-character categories. There have been no changes between the topography of ICD-O-2 and ICD-O-3.
• Morphology - Numerical List
  Morphology terms have five-digit codes ranging from M-8000/0 to M-9989/3. The first four digits indicate the specific histologic term. The fifth digit, after the slash or solidus (/), is a behavior code, which indicates whether a tumor is malignant, benign, in situ, or uncertain whether malignant or benign.
  A separate one-digit code for histologic grading or differentiation is provided. For a lymphoma or leukemia, this element of the code is used to identify T-, B-, Null-, and NK-cell origin.
  
• Alphabetic Index
  The alphabetic index is used to code both topography (anatomical sites) and morphology (histologic terms). The index also includes selected tumor-like lesions and conditions. Topography codes are identified by the letter C, the first character of codes in Chapter II of ICD-10. The prefix M is used to identify morphology codes. The terms are listed under both the noun and the adjective. For example, basophil adenocarcinoma is listed under B for "basophil" and under A for "adenocarcinoma, basophil".
  
• Differences in Morphology Codes between Second and Third Editions
  This section consists of a list of terms now considered malignant, a list of all new morphology code numbers and a list of all terms and synonyms added to existing code definitions.