ICD-10 Code C18.8 – Malignant neoplasm of overlapping sites of colon (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C18.8 – Malignant neoplasm of overlapping sites of colon
What it is
C18.8 identifies a malignant tumor of the colon that spans overlapping contiguous sites, making a single primary location hard to assign. Use this code when the record clearly states overlapping sites of the colon.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include abdominal pain, change in bowel habits, rectal bleeding, anemia, or weight loss, but the diagnosis should be supported by pathology, imaging, or specialist assessment.
When to use this code
Use C18.8 when the provider documents a colon cancer involving overlapping adjacent segments, such as a lesion crossing two named sites. It is appropriate when no single subsite is identified and the record specifically supports “overlapping sites.”
If the note only says “colon cancer” without a more specific location, check documentation before selecting this code. Code the most specific documented site when available.
Do not use for
Do not use C18.8 for cancers limited to one colon subsite, such as cecum, sigmoid colon, or transverse colon. Do not use it when the documentation is unclear; check documentation.
Coding tip
Assign C18.8 only when the provider explicitly documents overlapping colon sites; otherwise, query for a more specific site.