ICD-10 Code C18.9 – Malignant neoplasm of colon, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C18.9 – Malignant neoplasm of colon, unspecified
What it is
C18.9 identifies a malignant tumor of the colon when the specific colon site is not documented. Use it for primary colon cancer with no further anatomic detail.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include change in bowel habits, rectal bleeding, abdominal pain, anemia, or weight loss, but the record must support malignancy of the colon.
When to use this code
Use C18.9 when the provider documents colon cancer but does not specify the cecum, ascending, transverse, descending, sigmoid, or overlapping site. It is also appropriate when the chart confirms a malignant neoplasm of the colon without more detail.
If later documentation identifies the exact colon location, code the more specific site instead. Check whether the cancer is primary, recurrent, or metastatic, because those details can affect coding.
Do not use for
Do not use this code for benign colon polyps, carcinoma in situ, or malignancy of the rectum, anus, or small intestine. Check documentation if the primary site is elsewhere.
Coding tip
Query for the exact colon subsite whenever the record only says “colon cancer” and the location is unclear.