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ICD-10-CM 2027 diagnosis code

C21Malignant neoplasm of anus and anal canal

Not billable — use a more specific code

C21 is a header code, so it can't be reported by itself. Choose one of the 4 more specific codes beneath it.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About C21

C21 is the ICD-10-CM diagnosis code for malignant neoplasm of anus and anal canal. It belongs to block C15-C26 (malignant neoplasms of digestive organs) and chapter 2 (neoplasms). It is a header code, so it can't be reported by itself; one of its 4 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: C21.0 (unspecified), C21.1 (canal), C21.2 (zone) and C21.8 (canal).

The conditions in its Excludes2 note aren't part of C21, but may be coded alongside it if the patient has both: 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) and 3 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under C21

Coding notes

Excludes2Not included here — may be reported together if both conditions exist

Notes that apply from higher levels

Instructions written at a parent level also apply to C21.

Broader instructions also apply from C15-C26 Malignant neoplasms of digestive organs and Chapter 2: Neoplasms.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about C21

Is C21 billable?

No. C21 is a header code. Report one of its more specific subcodes instead.