2026 ICD-10-CM Diagnosis Code C21.8Malignant neoplasm of overlapping sites of rectum, anus and anal canal
ICD-10-CM Codes›C00–D49›C15-C26›C21
- Billable — Valid for Submission
- Chronic Condition
C21.8 is a billable ICD-10-CM diagnosis code for malignant neoplasm of overlapping sites of rectum, anus and anal canal. 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. Coders also document this condition as anorectal adenocarcinoma. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Gastrointestinal cancers - anus.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Anorectal adenocarcinoma
- Malignant neoplasm of anorectal junction
- Malignant neoplasm of anorectum
- Overlapping malignant neoplasm of rectum, anus and anal canal
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Malignant neoplasm of anorectal junction
- Malignant neoplasm of anorectum
- Primary malignant neoplasm of two or more contiguous sites of rectum, anus and anal canal
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Table of NeoplasmsClinical
Anatomical sites in the Table of Neoplasms that reference this code family.
| Site | Malig. Primary | Malig. Secondary | Ca in situ | Benign | Uncertain | Unspec. |
|---|---|---|---|---|---|---|
| anorectum, anorectal (junction) | C21.8 | C78.5 | D01.3 | D12.9 | D37.8 | D49.0 |
| anus, anal › overlapping lesion with rectosigmoid junction or rectum | C21.8 | – | – | – | – | – |
| crypt of Morgagni | C21.8 | C78.5 | D01.3 | D12.9 | D37.8 | D49.0 |
| junction | C21.8 | C78.5 | D01.3 | D12.9 | D37.8 | D49.0 |
| junction › anorectal | C21.8 | C78.5 | D01.3 | D12.9 | D37.8 | D49.0 |
| rectosigmoid (junction) › overlapping lesion with anus or rectum | C21.8 | – | – | – | – | – |
| rectum (ampulla) › overlapping lesion with anus or rectosigmoid junction | C21.8 | – | – | – | – | – |
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 C21.8 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C21.8Overview
Is C21.8 (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 overlapping sites of rectum, anus and anal canal on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C21.8 group to?
When malignant neoplasm of overlapping sites of rectum, anus and anal canal 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 C21.8?
Under the General Equivalence Mappings, malignant neoplasm of overlapping sites of rectum, anus and anal canal converts to ICD-9-CM 154.8 (mal neo rectum/anus NEC). The mapping is approximate, so confirm the match fits the documentation.
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.
