C21.0 Malignant neoplasm of anus, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from C21 Malignant neoplasm of anus and anal canal

Excludes2 (not included here)

• 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)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 22 — Bladder, Colorectal, and Other Cancers
• CMS-HCC V22: HCC 11 — Colorectal, Bladder, and Other Cancers
• ESRD V24: HCC 11

MS-DRG index

Defines the logic of DRG(s) 374-376 in MDC 06.

Approximate ICD-9-CM (GEMs)

• 154.3 Malignant neoplasm of anus, unspecified site

Code annotations containing back-references to C21.0

Back-references to C21.0

• Type 2 Excludes: C43.5 Malignant melanoma of trunk ("malignant neoplasm of anus NOS (C21.0)")
• Type 2 Excludes: C4A.5 Merkel cell carcinoma of trunk ("malignant neoplasm of anus NOS (C21.0)")
• Type 1 Excludes: C44.5 Other and unspecified malignant neoplasm of skin of trunk ("anus NOS (C21.0)")

Diagnosis Index entries for C21.0

• Paget's disease › extramammary › anus

Nearby codes

• C21 Malignant neoplasm of anus and anal canal
• C21.0 Malignant neoplasm of anus, unspecified (this code)
• C21.1 Malignant neoplasm of anal canal
• C21.2 Malignant neoplasm of cloacogenic zone
• C21.8 Malignant neoplasm of overlapping sites of rectum, anus and anal canal