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C43.122 ICD-10-CM Code: Malignant melanoma of left lower eyelid, including canthus

C43.122 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 · free HCC 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 lookupC43.122

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

C43.122

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

Malignant melanoma of left lower eyelid, including canthus

A type of skin cancer (melanoma) that starts in the left lower eyelid, including the corner of the eye where the eyelids meet.

Buddy the Bee presenting code insight

Buddy Insight

Malignant melanoma of the left lower eyelid, including the canthus.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 23

Code-level coefficient reference

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
C43.1Malignant melanoma of eyelid, including canthusC43.12Malignant melanoma of left eyelid, including canthusC43.122Malignant melanoma of left lower eyelid, including canthus

Inclusion Terms

Official

No inclusion terms are included in this display for C43.122. Check the code and parent instructions in the Code Book.

Excludes 2

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

Related Codes

Official
C43.121Malignant melanoma of left upper eyelid, including canthus

Includes

Official

No Includes notes are included in this display for C43.122. 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 C43.122. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C43.122. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C43.122. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Left side and lower eyelid explicitly documented
Breslow depth and Clark level of invasion
Ulceration and mitotic rate
Lacrimal system involvement

MEAT Support

HCC Buddy guidance
Left side and lower eyelid explicitly documented
Breslow depth and Clark level of invasion
Ulceration and mitotic rate
Lacrimal system involvement

Audit Caution

HCC Buddy guidance
Defaulting to a less specific eyelid code when this 7-character code is supported by documentation
Confusing melanoma of the lower eyelid with melanoma of the cheek or malar area
Using this code for melanoma in situ which requires D03.122
Failing to distinguish between skin melanoma of the eyelid and conjunctival melanoma (C69.0)

Common Mistakes

HCC Buddy guidance
C43.121 — Melanoma of left UPPER eyelid; upper vs. lower distinction
C43.112 — Melanoma of RIGHT lower eyelid; laterality differentiation
C43.10 — Melanoma of UNSPECIFIED eyelid; avoid when left lower is documented
C44.122 — Other skin cancer of left lower eyelid; for basal cell or squamous cell carcinoma

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 C43.122 an HCC code?

Yes. C43.122 (Malignant melanoma of left lower eyelid, including canthus) 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: C43.122 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
C43.122
Description
Malignant melanoma of left lower eyelid, including canthus
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 C43.122 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C43.122

For C43.122, 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

C43.122 is the ICD-10-CM diagnosis code for malignant melanoma of left lower eyelid, including canthus. A type of skin cancer (melanoma) that starts in the left lower eyelid, including the corner of the eye where the eyelids meet. C43.122 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, C43.122 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 C43.122; 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 left lower eyelid location to ensure correct code selection. For C43.122, 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 C43.122 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Verify documentation specifies left lower eyelid location to ensure correct code selection
  • •Distinguish between upper (C43.121) and lower eyelid locations as they have different codes

Clinical Significance

Malignant melanoma of the left lower eyelid, including the canthus. This code represents the maximum level of specificity for this anatomic site. Lower eyelid melanomas require careful attention to reconstructive technique to maintain eyelid function, tear drainage, and cosmesis after adequate surgical excision.

Documentation Requirements

  • ✓Left side and lower eyelid explicitly documented
  • ✓Breslow depth and Clark level of invasion
  • ✓Ulceration and mitotic rate
  • ✓Lacrimal system involvement
  • ✓Sentinel lymph node biopsy results
  • ✓AJCC staging and treatment plan

Commonly Confused Codes

  • •C43.121: Melanoma of left UPPER eyelid; upper vs. lower distinction
  • •C43.112: Melanoma of RIGHT lower eyelid; laterality differentiation
  • •C43.10: Melanoma of UNSPECIFIED eyelid; avoid when left lower is documented
  • •C44.122: Other skin cancer of left lower eyelid; for basal cell or squamous cell carcinoma

Child Codes

C43.121Malignant melanoma of left upper eyelid, including canthus
HCC 23
C43.122Malignant melanoma of left lower eyelid, including canthus
HCC 23

Code Hierarchy

└C43Malignant melanoma of skin└C43.1Malignant melanoma of eyelid, including canthus└C43.12Malignant melanoma of left eyelid, including canthus└C43.122Malignant melanoma of left lower eyelid, including canthus
└C43.122Malignant melanoma of left lower eyelid, including canthus

C43.122 code history

Code setChange
FY2019 (effective Oct 1, 2018)Added to the code set

Source: official CMS ICD-10-CM order and addenda files, FY2016 through FY2027.

For C43.122, 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.

C43.122 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 C43.122. 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.

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