Is ICD-10-CM code C21 billable?

No, C21 (Malignant neoplasm of anus and anal canal) is a non-billable ICD-10-CM code. It must be coded to a more specific subcategory before it can be used for reimbursement.

What chapter does ICD-10-CM code C21 belong to?

C21 belongs to Chapter 2 of the ICD-10-CM tabular list: C00–D49 (Neoplasms).

C21Not billable, use a more specific code below

Malignant neoplasm of anus and anal canal

In Malignant neoplasms of digestive organs (C15-C26), chapter 2: Neoplasms

4 billable codes under C21: all are a CC; all map to HCC 22 (Bladder, Colorectal, and Other Cancers).A CC or MCC (major CC) is a secondary diagnosis that raises the MS-DRG payment. An HCC counts toward a Medicare Advantage patient's risk score.

Instructional notes

Excludes2: not included here, code separately if applicable

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)

Also applies, from Malignant neoplasms of digestive organs (C15-C26)

These notes sit on C15-C26 and apply to every code under it, including C21.

Excludes1: not coded here, use a different code

Kaposi's sarcoma of gastrointestinal sites (C46.4)

Excludes2: not included here, code separately if applicable

gastrointestinal stromal tumors (C49.A-)

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

Rules for coding benign and malignant neoplasms: using the Neoplasm Table, sequencing primary and secondary sites, treatment encounters, complications, and current cancer versus personal history.

Admission/Encounter for treatment of primary site (page 33)
Admission/Encounter for treatment of secondary site (page 33)
Coding and sequencing of complications (page 34)
Primary malignancy previously excised (page 34)
Admissions/Encounters involving antineoplastic chemotherapy, immunotherapy and radiation therapy (page 35)
Admission/encounter to determine extent of malignancy (page 36)
Symptoms, signs, and abnormal findings listed in Chapter 18 associated with neoplasms (page 36)
Admission/encounter for pain control/management (page 36)

Read Section I.C.2 (page 32), 12 more topics

All codes under C21

C21 can't be used on a claim. Pick a billable code below; grey headings group them.

C21 MS-DRGs

As the principal diagnosis, all 4 billable codes under C21 group to MS-DRG 374, 375, or 376 (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.

Other codes that refer to C21

Notes on these codes point to C21.

Z85.048 Includes: Conditions classifiable to C19-C21

About the condition

Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.

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.

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.