C4A.39
BillableMerkel cell carcinoma of other parts of face
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C4A.39 an HCC code?
Yes. C4A.39 maps to Lymphoma and Other 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 C4A.39
For C4A.39to 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 C4A.39 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C4A.39 is the ICD-10-CM diagnosis code for merkel cell carcinoma of other parts of face. Merkel cell carcinoma is a rare and aggressive skin cancer that develops on the face in areas not specifically identified as the nose, ear, or lip. This type of cancer arises from neuroendocrine cells in the skin and typically appears as a firm, painless nodule. C4A.39 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, C4A.39 maps to Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older CMS-HCC V24 model, C4A.39 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.
Verify the exact anatomical location on the face documented by the provider; if the site is nose, ear, or lip, use more specific codes (C4A.31, C4A.32, or C4A.33) instead of C4A.39. Because C4A.39 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 C4A.39 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the exact anatomical location on the face documented by the provider; if the site is nose, ear, or lip, use more specific codes (C4A.31, C4A.32, or C4A.33) instead of C4A.39
- •Confirm whether this is the initial diagnosis or a recurrent/metastatic presentation, as this may affect staging and treatment coding; always link to the appropriate laterality code if applicable
Clinical Significance
Merkel cell carcinoma of other parts of face covers facial locations not specifically classified elsewhere — such as the cheek, forehead, temple, chin, or perioral area. This is an aggressive neuroendocrine skin malignancy in a cosmetically and functionally important region. Facial Merkel cell carcinoma carries high metastatic potential due to the extensive lymphatic network of the head and neck.
Documentation Requirements
- ✓Histopathologic confirmation of Merkel cell carcinoma
- ✓Specific facial subsite documented (cheek, forehead, temple, chin, perioral region)
- ✓Confirmation that the site is NOT the nose (C4A.31), eyelid (C4A.1x), or ear (C4A.2x)
- ✓Tumor dimensions, depth, and margin status
- ✓Lymph node assessment (cervical, parotid, submandibular)
- ✓Treatment plan documentation
Commonly Confused Codes
- •C4A.30 — Merkel cell carcinoma of unspecified face; use C4A.39 when a specific non-nose site is documented
- •C4A.31 — Merkel cell carcinoma of nose; use for nasal-specific lesions
- •C4A.4 — Merkel cell carcinoma of scalp and neck; for lesions above the hairline or on the neck, not face
- •C44.39x — Other malignant neoplasm of other parts of face skin; not Merkel cell
- •C43.39 — Melanoma of other parts of face; different tumor histology