California Cancer Reporting System Standards Volume I: Abstracting and Coding Procedures
This instruction discusses how to code specific categories in instances where a specific primary site cannot be identified.
Assign codes from the following categories only when the primary site cannot be identified exactly:
NOS (not otherwise specified) subcategory when a subsite or tissue of an organ is not specifically listed in ICD-O-3.
Do not use NOS if a more descriptive term is available.
Use Codes C76.0 - C76.8 for diagnoses referring to regions and ill defined sites of the body, such as "head", "thorax", "abdomen", "pelvis", "upper limb," and "lower limb".
These sites typically contain several types of tissue (e.g., bone, skin, soft tissue), which might not be specified on the diagnostic statement.
If the tissue in which the tumor originated can be identified, use a more specific site code.
Use Code C80.9 when the primary site is not known and the only information available is the, metastatic or secondary site.