C04.8
BillableMalignant neoplasm of overlapping sites of floor of mouth
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C04.8 an HCC code?
Yes. C04.8 maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers 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 C04.8
For C04.8to 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 C04.8 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C04.8 is the ICD-10-CM diagnosis code for malignant neoplasm of overlapping sites of floor of mouth. Cancer of the floor of mouth that involves multiple overlapping areas or sites within the floor of mouth region. C04.8 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lip, oral cavity and pharynx (c00-c14).
Under the CMS-HCC V28 risk adjustment model, C04.8 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, C04.8 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.307. 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.
Use when tumor crosses anatomical boundaries within floor of mouth. Because C04.8 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 C04.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use when tumor crosses anatomical boundaries within floor of mouth
- •Document all involved sites for treatment planning purposes
Clinical Significance
This overlapping sites code indicates a floor of mouth cancer that crosses anatomical boundaries between the anterior and lateral regions. Overlapping tumors tend to be more advanced at presentation and often require more extensive surgical resection, making accurate coding critical for reflecting true disease burden.
Documentation Requirements
- ✓Pathology report confirming malignancy across multiple floor of mouth subsites
- ✓Documentation explicitly describing involvement of more than one floor of mouth region
- ✓Imaging studies showing extent of tumor spread across anatomical boundaries
- ✓TNM staging reflecting the overlapping nature of the tumor
- ✓Surgical margins and extent of planned or completed resection
Commonly Confused Codes
- •C04.0 — Anterior floor of mouth; use when tumor is confined to anterior region only
- •C04.1 — Lateral floor of mouth; use when tumor is confined to lateral region only
- •C04.9 — Floor of mouth, unspecified; use only when documentation does not specify any subsite at all
- •C06.80 — Overlapping sites of unspecified parts of mouth; use when tumor crosses beyond floor of mouth into other oral structures