ICD-10 Code C21.1 – Malignant neoplasm of anal canal (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C21.1 – Malignant neoplasm of anal canal
What it is
C21.1 identifies a malignant tumor arising in the anal canal. Use it when the documentation specifically states cancer of the anal canal, not the anal margin or rectum.
Clinical signs
Clinical features vary; refer to documentation. Commonly documented findings include anal bleeding, pain, a palpable mass, or change in bowel habits, but the diagnosis must be confirmed by pathology or specialist assessment.
When to use this code
Use C21.1 when the provider documents primary cancer of the anal canal, including a biopsy-confirmed malignancy or a clearly stated diagnosis in the record. Code it for encounters focused on evaluation, staging, follow-up, or management of that specific tumor.
Do not use for
Do not use this code for malignant neoplasm of the anal margin, rectum, or other anorectal sites. If the site is unclear or mixed in the note, check documentation before assigning C21.1.
Coding tip
Confirm the exact anatomic site in the pathology or provider note before coding, because anal canal and anal margin are coded separately.