2026 ICD-10-CM Diagnosis Code C21.0Malignant neoplasm of anus, unspecified

ICD-10-CM Codes›C00–D49›C15-C26›C21

ICD-10-CM C21.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C21.0 is a billable ICD-10-CM diagnosis code for malignant neoplasm of anus, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 374 through 376. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Gastrointestinal cancers - anus.

Code Identity

ICD-10-CM Code
C21.0
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of anus, unspecified
Short Description
Malignant neoplasm of anus, unspecified
Same as the full description in the CMS dataset.
Parent Code
C21
Malignant neoplasm of anus and anal canal

Code Classification

ChapterC00–D49Neoplasms
SectionC15-C26Malignant neoplasms of digestive organs
CategoryC21Malignant neoplasm of anus and anal canal
This CodeC21.0Malignant neoplasm of anus, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adenocarcinoma of anus
  • Anorectal adenocarcinoma
  • Carcinoma of anus
  • Lymphoma of anus
  • Malignant mesenchymal neoplasm of anus
  • Malignant neoplasm of anus
  • Malignant neoplasm of rectosigmoid junction
  • Malignant neoplasm of rectum, rectosigmoid junction and anus
  • Primary adenocarcinoma of anus
  • Primary malignant mesenchymal neoplasm of anus
  • Primary malignant neoplasm of anus
  • Primary sarcoma of perineum
  • Primary squamous cell carcinoma of anus

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Paget's disease
      • extramammary
        • anus

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO016
Gastrointestinal cancers - anus
Default principal diagnosis: inpatient Yes · outpatient Yes

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
anus, analC21.0C78.5D01.3D12.9D37.8D49.0

Patient EducationClinical

Anal Cancer

Your anus is the opening at the end of your large intestine. It is where stool (poop) leaves your body. The anus is formed partly from your outer layers of skin and partly from your intestine. Anal cancer is a type of cancer that forms in the tissues of your anus.

The full article covers:

  • What is anal cancer?
  • Who is more likely to develop anal cancer?
  • What are the symptoms of anal cancer?
  • How is anal cancer diagnosed?
  • What are the treatments for anal cancer?
  • Can anal cancer be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert C21.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
154.3 Malignant neo anus NOS
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C21.0Overview

Is C21.0 (Malignant neoplasm of anus and anal canal) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of anus, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C21.0 group to?

When malignant neoplasm of anus, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 374, 375, 376, with relative weights from 0.9243 to 2.1387 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C21.0?

Under the General Equivalence Mappings, malignant neoplasm of anus, unspecified converts to ICD-9-CM 154.3 (malignant neo anus NOS). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.