General Rules

Coding Tumor Extension

1. This field represents distant metastases (the TNM M component or distant stage in Summary Staging) at the time of diagnosis. In other words, when the patient was diagnosed, tumor had already spread indirectly (through vascular or lymph channels) to a site remote from the primary tumor.
2. Metastasis known to have developed after the extent of disease was established (also referred to as progression of disease) should not be recorded in the CS Mets at DX field.
3. Record CS Mets at DX as Code 00 rather than Code 99 when the clinician proceeds with standard treatment of the primary site for localized or early (T1, T2) stage, since this action presumes that there are no distant metastasis that would otherwise alter the treatment approach. Code 99 can and should be used in situations where there is reasonable doubt that the tumor is no longer localized and there is no documentation of distant metastases.
4. If the only indication of extension in the record is the physician's statement of an M category from the TNM staging system or a stage from a site-specific staging system, such as Dukes' D, record the numerically lowest equivalent extension code for that M category. In most cases, this will be 40, Distant metastasis, NOS.
5. If the information in the medical record is ambiguous or incomplete regarding the extent to which the tumor has spread, the extent of disease may be inferred from the M category stated by the physician.
6. Some site or histology schemes include a designation of M1, NOS. The NOS is added when there is further breakdown of the category into subsets (such as M1a, M1b, M1c), but the correct subset cannot be determined.