2027 ICD-10-CM Diagnosis Code C21Malignant neoplasm of anus and anal canal

ICD-10-CM Codes›C00–D49›C15-C26›C21

ICD-10-CM C21
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

C21 is a non-billable ICD-10-CM category code for malignant neoplasm of anus and anal canal, so it cannot be submitted on claims. Use a more specific code from this category instead, such as C21.0, C21.1, C21.2, and C21.8.

Code Identity

ICD-10-CM Code
C21
Billable Status
No — Non-Billable Category
Code Describes
Malignant neoplasm of anus and anal canal
Short Description
Malignant neoplasm of anus and anal canal
Same as the full description in the CMS dataset.
Chapter
C15-C26
Malignant neoplasms of digestive organs

Code Classification

ChapterC00–D49Neoplasms
SectionC15-C26Malignant neoplasms of digestive organs
CategoryC21Malignant neoplasm of anus and anal canal
This CodeC21Malignant neoplasm of anus and anal canal

Specific Coding for Malignant neoplasm of anus and anal canalOverview

Non-specific codes like C21 require more characters. Use one of these billable codes instead:

  • Use C21.0 for Malignant neoplasm of anus, unspecified

  • Use C21.1 for Malignant neoplasm of anal canal

  • Use C21.2 for Malignant neoplasm of cloacogenic zone

  • Use C21.8 for Malignant neoplasm of overlapping sites of rectum, anus and anal canal

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to C21: its own notes plus those printed at block C15-C26 and Chapter 2. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Block C15-C26 Malignant neoplasms of digestive organs applies to 60 codes
  • Kaposi's sarcoma of gastrointestinal sites (C46.4)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

On C21 itself
From Block C15-C26 Malignant neoplasms of digestive organs applies to 60 codes
  • gastrointestinal stromal tumors (C49.A-)

Notes

General instructions on how these codes are used.

From Chapter 2 (C00-D49) Neoplasms applies to 1,730 codes
  • Functional activity
  • All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
  • Morphology [Histology]
  • Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
  • Primary malignant neoplasms overlapping site boundaries
  • A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
  • Malignant neoplasm of ectopic tissue
  • Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name C21, its category, or a range that includes it.

Applicable To 2

These notes mention C21.

  • Z80.0 Family history of malignant neoplasm of digestive organs
    Conditions classifiable to C15-C26 names C15-C26, which includes this code
  • Z85.048 Personal history of other malignant neoplasm of rectum, rectosigmoid junction, and anus
    Conditions classifiable to C19-C21 names C19-C21, which includes this code

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.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About C21Overview

What is the ICD-10 code for malignant neoplasm of anus and anal canal?

C21 is the ICD-10-CM category for malignant neoplasm of anus and anal canal, but it is a non-billable header: claims need a more specific code from this category, listed on this page.

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

No. This is a category header that groups the codes for malignant neoplasm of anus and anal canal, and headers cannot be submitted on claims. Claims for malignant neoplasm of anus and anal canal need a more specific code from this category, such as C21.0, C21.1, and C21.2.

Can C21 be reported with C46.4?

Not as a rule. The Excludes1 note at block C15-C26, which applies to C21, lists "Kaposi's sarcoma of gastrointestinal sites (C46.4)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).