C21.0 — Malignant neoplasm of anus, unspecified
C21.0 is a billable, specific ICD-10-CM code for malignant neoplasm of anus, unspecified. It is valid for submission on a claim.
Excludes2 inherited from the categories above C21.0
Also inherited, and the opposite of Excludes1: these conditions are not part of C21.0, but a patient can have both, so you may code both.
Written on C21 — Malignant neoplasm of anus and anal canal
- malignant carcinoid tumors of the colon (C7A.02-)
- malignant melanoma of anal margin (C43.51)
- malignant melanoma of anal skin (C43.51)
- malignant melanoma of perianal skin (C43.51)
- other and unspecified malignant neoplasm of anal margin (C44.500, C44.510, C44.520, C44.590)
- other and unspecified malignant neoplasm of anal skin (C44.500, C44.510, C44.520, C44.590)
- other and unspecified malignant neoplasm of perianal skin (C44.500, C44.510, C44.520, C44.590)
Other codes that can never be billed with C21.0
These codes carry an Excludes1 note pointing at C21.0. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading C21.0 alone.
- C44.5Other and unspecified malignant neoplasm of skin of trunk
Risk adjustment
C21.0 risk-adjusts. Under the CMS-HCC V28 model it maps to this category:
- HCC 22 Bladder, Colorectal, and Other Cancers0.363 RAF
Coefficient shown for the Community Non-dual Aged segment. A higher HCC in the same hierarchy will suppress this one, so capturing it does not always add score.
Medicare coverage
C21.0 is named in 67 Medicare coverage policies — 67 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A52450Billing and Coding: Paclitaxel (e.g., Taxol®/Abraxane ™)
- A52450Billing and Coding: Paclitaxel (e.g., Taxol®/Abraxane ™)
- A52479Oral Anticancer Drugs - Policy Article
- A52479Oral Anticancer Drugs - Policy Article
How C21.0 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to C21.0.
- Paget's disease›extramammary›anus
Code history
C21.0 has not changed since FY2024 — no addition, revision or deletion across the three most recent ICD-10-CM releases.
Related codes at this level
Codes that share C21. If C21.0 is not quite right, the correct code is usually one of these.
Questions about C21.0
- Is C21.0 a billable ICD-10-CM code?
- Yes. C21.0 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does C21.0 sit in the tabular list?
- Neoplasms (C00-D49), in the block Malignant neoplasms of digestive organs (C15-C26).