C43.121 ICD-10-CM Code: Malignant melanoma of left upper eyelid, including canthus
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Neoplasms (C00-D49) / Melanoma and other malignant neoplasms of skin (C43-C44)
C43.121
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant melanoma of left upper eyelid, including canthus
A type of skin cancer (melanoma) that starts in the left upper eyelid, including the corner of the eye where the eyelids meet.
Buddy Insight
Malignant melanoma of the left upper eyelid, including the canthus.
CMS-HCC V28
MappedHCC 23
RAF 0.251
CMS-HCC V24
MappedHCC 12
RAF 0.150
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 12
RAF 0.0
RXHCC
MappedHCC 22
RAF 0.0
Code Trumping
Basket needed
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for C43.121 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C43.121 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for C43.121 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for C43.121 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for C43.121 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for C43.121 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for C43.121 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is C43.121 an HCC code?
Yes. C43.121 maps to Melanoma and Other Skin Cancers under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C43.121
For C43.121to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.
- 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
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C43.121 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
C43.121 is the ICD-10-CM diagnosis code for malignant melanoma of left upper eyelid, including canthus. A type of skin cancer (melanoma) that starts in the left upper eyelid, including the corner of the eye where the eyelids meet. C43.121 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, C43.121 maps to Melanoma and Other Skin Cancers (HCC 23) with a community, non-dual, aged base RAF weight of 0.251. Under the older CMS-HCC V24 model, C43.121 maps to Breast, Prostate, and Other Cancers and Tumors (HCC 12) with a community, non-dual, aged base RAF weight of 0.150. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Confirm left side laterality is documented to differentiate from right upper eyelid (C43.111). Because C43.121 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for C43.121 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm left side laterality is documented to differentiate from right upper eyelid (C43.111)
- •Note that 'including canthus' means the inner or outer corner of the eye is involved in the melanoma
Clinical Significance
Malignant melanoma of the left upper eyelid, including the canthus. Like other periocular melanomas, this carries risks of orbital invasion and requires careful surgical planning with sentinel lymph node evaluation. The left laterality and upper eyelid specification provide maximum coding precision.
Documentation Requirements
- ✓Left side and upper eyelid explicitly documented
- ✓Breslow depth (thickness in millimeters)
- ✓Ulceration status and mitotic rate
- ✓Canthus involvement (medial or lateral) if applicable
- ✓Sentinel lymph node biopsy of parotid and cervical basins
- ✓AJCC staging and treatment plan
Commonly Confused Codes
- •C43.122 — Melanoma of left LOWER eyelid; upper vs. lower distinction
- •C43.111 — Melanoma of RIGHT upper eyelid; laterality differentiation
- •C43.10 — Melanoma of UNSPECIFIED eyelid; avoid when left upper is documented
- •D03.121 — Melanoma in situ of left upper eyelid; non-invasive, different HCC mapping