ICD-10 Code C79.9 – Secondary malignant neoplasm of unspecified site (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C79.9 – Secondary malignant neoplasm of unspecified site
What it is
C79.9 identifies metastatic cancer when the secondary site is not specified in the documentation. Use it for a malignant neoplasm that has spread, but the exact organ or tissue involved is not named.
Clinical signs
Clinical features vary; refer to documentation. Findings may reflect metastatic disease at an unspecified location, such as a known primary cancer with evidence of spread, but no documented site detail.
When to use this code
Use this code when the record clearly states secondary malignant neoplasm and does not identify the involved site. It may apply when imaging, pathology, or provider notes confirm metastasis, but the location remains unspecified. You should code the documented primary malignancy separately when available.
Do not use for
Do not use C79.9 when the metastatic site is documented; choose the more specific secondary site code instead. Do not use it for a primary malignancy, suspected cancer, or history of cancer without active metastatic disease.
Coding tip
Check the chart for a more specific metastatic site before assigning C79.9, because unspecified codes should be used only when documentation lacks detail.