ICD-10 Code C80.1 – Malignant (primary) neoplasm, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C80.1 – Malignant (primary) neoplasm, unspecified
What it is
C80.1 identifies a primary malignant cancer when the site of origin is not documented or cannot be determined. Use it only when the record clearly supports a primary malignancy but does not name the anatomic location.
Clinical signs
Clinical features vary; refer to documentation. Common presentations may include nonspecific cancer findings, but the diagnosis must be supported by pathology, imaging, or provider assessment that indicates a primary malignant neoplasm.
When to use this code
Use this code when the provider documents a primary malignancy and the primary site remains unspecified after review of the available record. It may also apply when the cancer is confirmed, but the source site is not yet identified. If later documentation names the primary site, code that more specific diagnosis instead.
Do not use for
Do not use C80.1 for metastatic disease, secondary malignancy, or carcinoma in situ. If the record identifies a primary site or only says “history of cancer,” choose the more specific or appropriate history code.
Coding tip
Query the provider if the chart suggests a primary cancer but the site is missing, because unspecified should be a last resort.