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C43.51 ICD-10-CM Code: Malignant melanoma of anal skin

C43.51 maps to CMS-HCC V28 23. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools

ICD-10-CM Code View

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Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC43.51

FY 2026 Apr update / Neoplasms (C00-D49) / Melanoma and other malignant neoplasms of skin (C43-C44)

C43.51

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant melanoma of anal skin

A type of skin cancer (melanoma) that develops on the skin around the anus. This is a serious form of cancer that requires prompt treatment.

Buddy the Bee presenting code insight

Buddy Insight

Malignant melanoma of anal skin (perianal skin).

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 23

Coefficient HCC 23: 0.186 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 013

Code-level coefficient reference

ESRD/PACE

HCC 12

Code-level coefficient reference

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C43Malignant melanoma of skinC43.5Malignant melanoma of trunkC43.51Malignant melanoma of anal skin

Inclusion Terms

Official
  • Malignant melanoma of anal margin
  • Malignant melanoma of perianal skin

Excludes 2

Official
  • malignant melanoma of skin of genital organs (C51-C52, C60.-, C63.-)Inherited from C43, C43.5
  • Merkel cell carcinoma (C4A.-)Inherited from C43, C43.5
  • sites other than skin-code to malignant neoplasm of the siteInherited from C43, C43.5
  • malignant neoplasm of anus NOS (C21.0)Inherited from C43, C43.5
  • malignant neoplasm of scrotum (C63.2)Inherited from C43, C43.5

Related Codes

Official
C43.52Malignant melanoma of skin of breastC43.59Malignant melanoma of other part of trunk

Includes

Official

No Includes notes are included in this display for C43.51. Check the code and parent instructions in the Code Book.

Excludes 1

Official
  • melanoma in situ (D03.-)Inherited from C43

Code First

Official

No Code First sequencing instructions are included in this display for C43.51. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C43.51. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C43.51. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Confirmation the melanoma is on the perianal SKIN, not the anal canal mucosa
Breslow depth and ulceration status
Relationship to the dentate line (above = mucosal/anal canal; below = perianal skin)
Sentinel lymph node biopsy results (inguinal nodes for perianal skin)

MEAT Support

HCC Buddy guidance
Confirmation the melanoma is on the perianal SKIN, not the anal canal mucosa
Breslow depth and ulceration status
Relationship to the dentate line (above = mucosal/anal canal; below = perianal skin)
Sentinel lymph node biopsy results (inguinal nodes for perianal skin)

Audit Caution

HCC Buddy guidance
Confusing perianal skin melanoma (C43.51) with mucosal anorectal melanoma (C21.1) — these are different diseases with different treatments and prognoses
Not distinguishing this from benign pigmented perianal lesions
Coding this as trunk melanoma (C43.59) when perianal skin has its own specific code
Misidentifying melanoma as a thrombosed hemorrhoid — any dark perianal lesion should be biopsied

Common Mistakes

HCC Buddy guidance
C21.0 — Malignant neoplasm of anus, unspecified; for non-melanoma anal cancer or when mucosal vs. skin is unclear
C21.1 — Malignant neoplasm of anal canal; for mucosal melanoma of the anal canal, which is a different disease
C43.59 — Melanoma of other part of trunk; perianal skin is specifically coded under C43.51
C43.52 — Melanoma of skin of breast; different trunk site

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C43.51 an HCC code?

Yes. C43.51 (Malignant melanoma of anal skin) maps to HCC 23, Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.186. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C43.51 is billable and maps to V28 HCC 23, Prostate, Breast, and Other Cancers and Tumors. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C43.51
Description
Malignant melanoma of anal skin
HCC (V28)
HCC 23 — Prostate, Breast, and Other Cancers and Tumors
RAF reference coefficient
0.186
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors
0.186
ESRDHCC 12, Breast/Prostate/and Other Cancers and Tumors
Not separately weighted
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C43.51 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C43.51

For C43.51, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
  • EEvaluate: test results, medication response, or physical findings reviewed by the provider
  • AAssess: explicit mention in the assessment or plan with acknowledgment of status
  • TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

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What This Code Means

C43.51 is the ICD-10-CM diagnosis code for malignant melanoma of anal skin. A type of skin cancer (melanoma) that develops on the skin around the anus. This is a serious form of cancer that requires prompt treatment. C43.51 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering melanoma and other malignant neoplasms of skin (c43-c44).

Under the CMS-HCC V28 risk adjustment model, C43.51 maps to Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a source-labeled community, non-dual, aged reference coefficient of 0.186. No V24 mapping is shown for C43.51; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Verify documentation specifies anal skin location to distinguish from rectal melanoma (C43.8 or other codes). For C43.51, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for C43.51 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Verify documentation specifies anal skin location to distinguish from rectal melanoma (C43.8 or other codes)
  • •Ensure laterality is not applicable for this midline anatomical location

Clinical Significance

Malignant melanoma of anal skin (perianal skin). This is distinct from mucosal melanoma of the anal canal, which is a much rarer and more aggressive disease. Perianal skin melanoma presents as a pigmented lesion near the anus and may be initially mistaken for hemorrhoids or a thrombosed external hemorrhoid. Early detection is critical.

Documentation Requirements

  • ✓Confirmation the melanoma is on the perianal SKIN, not the anal canal mucosa
  • ✓Breslow depth and ulceration status
  • ✓Relationship to the dentate line (above = mucosal/anal canal; below = perianal skin)
  • ✓Sentinel lymph node biopsy results (inguinal nodes for perianal skin)
  • ✓AJCC staging
  • ✓Treatment plan (wide local excision vs. abdominoperineal resection)

Commonly Confused Codes

  • •C21.0: Malignant neoplasm of anus, unspecified; for non-melanoma anal cancer or when mucosal vs. skin is unclear
  • •C21.1: Malignant neoplasm of anal canal; for mucosal melanoma of the anal canal, which is a different disease
  • •C43.59: Melanoma of other part of trunk; perianal skin is specifically coded under C43.51
  • •C43.52: Melanoma of skin of breast; different trunk site

Child Codes

C43.51Malignant melanoma of anal skin
HCC 23
C43.52Malignant melanoma of skin of breast
HCC 23
C43.59Malignant melanoma of other part of trunk
HCC 23

Code Hierarchy

└C43Malignant melanoma of skin└C43.5Malignant melanoma of trunk└C43.51Malignant melanoma of anal skin
└C43.51Malignant melanoma of anal skin

Also searched as

  • C43 51
  • C4351

For C43.51, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

C43.51 maps to CMS-HCC V28 category 23, Prostate, Breast, and Other Cancers and Tumors. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C43.51. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work C43.51 in HCC Buddy

Open C43.51 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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