C79.9
BillableSecondary malignant neoplasm of unspecified site
HCC Category Mapping
V28HCC 18 — Metastatic Cancer to Peritoneum and Other Specified Sites
0.368V24HCC 8 — Metastatic Cancer and Acute Leukemia
2.484ESRDHCC 8 — Metastatic Cancer and Acute Leukemia
0.000RxHCCHCC 18 — Metastatic Cancer to Lung and Other Respiratory Sites
0.000What This Code Means
Cancer that has spread to an unknown or unspecified location in the body from a primary cancer elsewhere.
Coding Tips
- •This is a non-specific code; use only when the secondary cancer site cannot be determined or is truly unspecified.
- •Query the provider if possible to identify the specific site of metastasis for more accurate coding.
Clinical Significance
Secondary malignant neoplasm of unspecified site indicates the patient has known metastatic cancer but the metastatic site cannot be identified or localized. This is the least specific secondary neoplasm code and should only be used when all attempts to identify the metastatic site have been exhausted. It may be appropriate when labs or tumor markers indicate metastatic disease but imaging has not yet localized the secondary site.
Documentation Requirements
- ✓Primary cancer site documented and coded separately, if known
- ✓Documentation of why the metastatic site cannot be determined
- ✓Evidence supporting the diagnosis of metastatic disease — rising tumor markers, clinical deterioration
- ✓Imaging studies performed and their findings
- ✓Provider query documenting inability to specify the metastatic site
Excludes 1 — Do NOT code together
Commonly Confused Codes
C79.89 — Secondary malignant neoplasm of other specified sites; use when the site IS known but has no specific codeC80.0 — Disseminated malignant neoplasm, unspecified; for widespread cancer without known primary or secondary sitesC80.1 — Malignant (primary) neoplasm, unspecified; this is for unknown PRIMARY site, not unknown secondary siteC76.0-C76.8 — Malignant neoplasm of other and ill-defined sites; these are primary ill-defined site codes
Code Hierarchy
└C79Secondary malignant neoplasm of other and unspecified sites└C79.9Secondary malignant neoplasm of unspecified site
└C79.9Secondary malignant neoplasm of unspecified site