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).