C04.0
BillableMalignant neoplasm of anterior floor of mouth
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C04.0 an HCC code?
Yes. C04.0 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 C04.0
For C04.0to 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 C04.0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C04.0 is the ICD-10-CM diagnosis code for malignant neoplasm of anterior floor of mouth. This code represents cancer that starts in the front part of the floor of the mouth, which is the tissue underneath the tongue. It is a malignant (spreading) tumor in this specific location. C04.0 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, C04.0 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, C04.0 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.
Ensure documentation specifies the anterior (front) floor of mouth location, as other floor of mouth sites have different codes (C04.1 for lateral floor, C04.8 for other/overlapping sites). Because C04.0 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 C04.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure documentation specifies the anterior (front) floor of mouth location, as other floor of mouth sites have different codes (C04.1 for lateral floor, C04.8 for other/overlapping sites)
- •Verify laterality is not applicable for this code; if the cancer involves multiple areas of the mouth floor, use C04.8 instead
Clinical Significance
Malignant neoplasm of the anterior floor of mouth is a clinically significant oral cancer arising in the tissue beneath the front portion of the tongue. This site is particularly important because cancers here may obstruct the sublingual salivary ducts and commonly present with early lymph node metastasis.
Documentation Requirements
- ✓Biopsy-confirmed malignancy with histological type
- ✓Specific documentation of 'anterior floor of mouth' location
- ✓TNM staging including depth of invasion and nodal status
- ✓Relationship to sublingual structures and mandible if applicable
- ✓Current treatment status: surgery, radiation, chemotherapy, or combination
Commonly Confused Codes
- •C04.1 — Lateral floor of mouth; differentiate anterior (front, midline area) from lateral (side) floor of mouth
- •C04.8 — Overlapping sites of floor of mouth; use when tumor crosses boundaries between anterior and lateral regions
- •C04.9 — Floor of mouth, unspecified; use only when anterior vs lateral cannot be determined
- •C02.1 — Malignant neoplasm of border of tongue; ventral tongue cancers may be confused with anterior floor of mouth