ICD-10 Code C18 – Malignant neoplasm of colon (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C18 – Malignant neoplasm of colon
What it is
C18 identifies a malignant neoplasm arising in the colon. Use it for documented primary colon cancer when the record does not specify a more exact colon site.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include change in bowel habits, abdominal pain, anemia, weight loss, or evidence of a colon mass on imaging or colonoscopy.
When to use this code
Use C18 when the provider documents colon cancer and does not name the cecum, ascending, transverse, descending, sigmoid, or overlapping site. It also fits cases where pathology or imaging confirms a malignant colon lesion but the exact segment is not stated.
Do not use for
Do not use C18 for malignant neoplasms of the rectum, rectosigmoid junction, anus, or small intestine. If the documentation gives a specific colon subsite, code that more precise diagnosis instead.
Coding tip
Check the operative note, pathology report, and final diagnosis for the exact colon location before assigning the unspecified code.