Secondary malignant neoplasm of unspecified site

This code signifies the presence of metastatic cancer where the primary tumor site is unknown, and the specific secondary site(s) are also not documented. It indicates that malignant cells have spread from an original, unidentified location to an unspecified part of the body.

Use this code when medical record documentation confirms a secondary malignant neoplasm but provides no further specificity regarding either the primary or secondary anatomical location. This is typically a last resort when all efforts to identify a more precise site have failed.

• Avoid using this code if any specific metastatic site (e.g., bone, lung, liver) is documented, even if the primary is unknown.
• Never code this with C80.0 (carcinomatosis NOS, generalized cancer NOS) or C80.1 (malignant primary neoplasm of unspecified site) due to Excludes1 notes.
• Prioritize codes that specify the secondary site (e.g., C79.51 for secondary malignant neoplasm of bone) whenever possible.