- Record the ICD-O-3 (International Classification of Diseases for Oncology, Third Edition) topography code for the site of origin.
- Consult the physician advisor to identify the primary site or the most definitive site code if the medical record does not contain that information.
- Primary site codes may be found in the ICD-O-3 Topography, Numerical List section (ICD-O-3, p. 43) and in the Alphabetic Index (ICD-O-3, p. 105).
- Topography codes are indicated by a "C" preceding the three-digit code number (do not record the decimal point).
- Follow the coding rules outlined in ICD-O-3, pp. 20-40.
- Use subcategory 8 for single tumors that overlap the boundaries of two or more sub-sites and the point of origin is not known.
- Use subcategory 9 for multiple tumors that originate in one organ.
- Code adenocarcinoma in multiple polyps as a single primary even if they involve more than one segment of the colon.
- Code leukemias to bone marrow (C42.1).
Exception: Code myeloid sarcoma to the site of origin (see ICD-O-3 for coding rules).
The ICD-O-3 is not publicly available for electronic download, but the manual can be borrowed from hospital registrars. The codes are similar to ICD-10, but not identical; they may be found in an appendix of some ICD-10 publications (not to be confused with the ICD-10-CM).