ICD-10 Code C21.8 – Malignant neoplasm of overlapping sites of rectum, anus and anal canal (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C21.8 – Malignant neoplasm of overlapping sites of rectum, anus and anal canal
What it is
C21.8 identifies a malignant tumor that spans overlapping parts of the rectum, anus, and anal canal. Use it when the primary site cannot be assigned to one single anatomic location.
Clinical signs
Clinical features vary; refer to documentation. Commonly documented findings may include rectal bleeding, pain, a mass, altered bowel habits, or abnormal endoscopic or biopsy results confirming malignancy.
When to use this code
Use this code when the provider documents cancer involving overlapping sites across the rectum, anus, and anal canal, or when pathology and imaging support a single lesion crossing these boundaries. It is appropriate when a more specific site is not documented. Check documentation if the record uses only one anatomic site.
Do not use for
Do not use C21.8 for a tumor clearly confined to the rectum, anus, or anal canal alone. Do not use it for benign, in situ, or metastatic disease unless the documentation specifically supports this primary site.
Coding tip
Assign C21.8 only when the record clearly shows overlapping anatomic involvement; otherwise code the single documented site.