ICD-10 Code C21.0 – Malignant neoplasm of anus, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C21.0 – Malignant neoplasm of anus, unspecified
What it is
C21.0 identifies a malignant tumor of the anus when the record does not specify the exact site or histology. Use this code for documented anal cancer with unspecified details.
Clinical signs
Clinical features vary; refer to documentation. Anal malignancy may present with rectal bleeding, pain, a mass, itching, or change in bowel habits, but the code itself depends on the documented diagnosis.
When to use this code
Use C21.0 when the provider documents malignant neoplasm of the anus and does not specify a more precise anal site or subtype. It is appropriate for confirmed cancer diagnoses in notes, pathology, or discharge summaries. If the record later specifies a different anal or rectal site, code that instead.
Do not use for
Do not use this code for benign anal lesions, hemorrhoids, fissures, or inflammatory anorectal disease. Also avoid it when the documentation identifies a more specific anal cancer code or a non-anal rectal malignancy.
Coding tip
Check the final pathology and provider assessment before assigning C21.0; if a more specific site is documented, code that instead.