ICD-10-CM 2027 diagnosis code
C21.1Malignant neoplasm of anal canal
C21.1 is a valid, billable ICD-10-CM code for malignant neoplasm of anal canal. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.
Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS, effective October 1, 2026. Updated September 29, 2026. About our data
About C21.1
C21.1 is the ICD-10-CM diagnosis code for malignant neoplasm of anal canal. It belongs to category C21 (malignant neoplasm of anus and anal canal), block C15-C26 (malignant neoplasms of digestive organs) and chapter 2 (neoplasms). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within C21 (malignant neoplasm of anus and anal canal), C21.1 is specifically for malignant neoplasm of anal canal. Related codes cover anus, unspecified (C21.0), cloacogenic zone (C21.2) and overlapping sites of rectum, anus and anal canal (C21.8).
As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 374 (Digestive Malignancy with MCC, relative weight 2.1109), DRG 375 (Digestive Malignancy with CC, relative weight 1.1838) and DRG 376 (Digestive Malignancy without CC/MCC, relative weight 0.8929), in MDC 06 (Diseases and Disorders of the Digestive System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Before ICD-10, this condition was coded in ICD-9-CM as 154.2 (malignant neoplasm of anal canal).
Coding notes
- Malignant neoplasm of anal sphincter
Notes that apply from higher levels
Instructions written at a parent level also apply to C21.1.
› From 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)
Broader instructions also apply from C15-C26 Malignant neoplasms of digestive organs and Chapter 2: Neoplasms.
Table of Drugs & Neoplasms entries
- Neoplasm, neoplastic › anus, anal › canal — Malignant Primary
- Neoplasm, neoplastic › anus, anal › sphincter — Malignant Primary
- Neoplasm, neoplastic › canal › anal — Malignant Primary
- Neoplasm, neoplastic › hemorrhoidal zone — Malignant Primary
- Neoplasm, neoplastic › sphincter › anal — Malignant Primary
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 06 · Diseases and Disorders of the Digestive System
ICD-9-CM equivalent
Converter →- 154.2Malignant neoplasm of anal canalexact
From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about C21.1
Is C21.1 billable?
- Yes. C21.1 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can C21.1 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict C21.1 as a principal diagnosis.
Is C21.1 a CC or MCC?
- C21.1 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.
What DRG does C21.1 group to?
- C21.1 is used in the MS-DRG v44.0 logic for MS-DRG 374 (Digestive Malignancy with MCC), MS-DRG 375 (Digestive Malignancy with CC) and MS-DRG 376 (Digestive Malignancy without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.
What is the ICD-9 code for C21.1?
- The CMS General Equivalence Mappings map C21.1 to ICD-9-CM 154.2.