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ICD-10 Code C21: Malignant neoplasm of anus and anal canal

C21 is an ICD-10 diagnosis entry used to group records related to Malignant neoplasm of anus and anal canal. You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen. ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Neoplasms (C00-D49).

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Neoplasms (C00-D49).

When is it used?

  • May be used when a clinician documents malignant neoplasm of anus and anal canal in a patient's medical record.
  • May appear in hospital records, claims, referrals, and clinical documentation.
  • This code may act more like a grouping or parent code, so a more specific child code may be used in final documentation when available.

What it does not mean

  • A code alone does not explain severity, treatment plan, or outcome.
  • A medical code should not be treated as a substitute for a doctor's diagnosis or advice.
  • This entry may represent a broader category rather than the most specific billable code.

Code hierarchy

chapter
2Neoplasms (C00-D49)
block
C00-C96Malignant neoplasms
block
C00-C75Malignant neoplasms, stated or presumed to be primary (of specified sites), and certain specified histologies, except neuroendocrine, and of lymphoid, hematopoietic and related tissue
block
C15-C26Malignant neoplasms of digestive organs
currentC15-C26

Official coding notes

Excludes2 (may code together if documented)
  • 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)

Where you may see this code

You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen.

Related specialists

OncologistGeneral Physician

Coding guidelines

Compatibility

Legacy code aligns to an official FY 2026 category. Frontend should resolve to the official category page and surface the billable child codes.
Legacy codes
C21
Replacement codes
C21.0 — Malignant neoplasm of anus, unspecifiedC21.1 — Malignant neoplasm of anal canalC21.2 — Malignant neoplasm of cloacogenic zoneC21.8 — Malignant neoplasm of overlapping sites of rectum, anus and anal canal

Common synonyms

Malignant neoplasm of anus and anal canal

Frequently asked questions

Code details

CodeC21
SystemICD10
Display nameMalignant neoplasm of anus and anal canal
ChapterNeoplasms (C00-D49)
BlockMalignant neoplasms of digestive organs

Flags

BillableNo
Valid clinical useNo

Source

SourceICD-10
Version2026-annual
Releaseannual
Year2026

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.

ICD-10 Code C21 for Malignant neoplasm of anus and anal canal | HealthAssure