C04.1
BillableMalignant neoplasm of lateral floor of mouth
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C04.1 an HCC code?
Yes. C04.1 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 C04.1
For C04.1to 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 C04.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C04.1 is the ICD-10-CM diagnosis code for malignant neoplasm of lateral floor of mouth. Cancer that develops on the side portion of the floor of the mouth, the soft tissue area beneath the tongue. C04.1 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, C04.1 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, C04.1 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.
Floor of mouth cancers often involve sublingual gland tissue. Because C04.1 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 C04.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Floor of mouth cancers often involve sublingual gland tissue
- •Confirm laterality (left vs right) when documented
Clinical Significance
Malignant neoplasm of the lateral floor of mouth involves cancer of the side portions of the tissue beneath the tongue. This location is clinically significant because the sublingual glands and Wharton's duct are in close proximity, and lateral floor tumors have a high propensity for submandibular lymph node metastasis.
Documentation Requirements
- ✓Pathology-confirmed malignancy with histological subtype
- ✓Documentation specifying lateral floor of mouth location
- ✓Laterality (left or right side) when documented
- ✓Depth of invasion and relationship to adjacent structures (sublingual gland, mandible)
- ✓Staging and current treatment plan
Commonly Confused Codes
- •C04.0 — Anterior floor of mouth; the anterior portion is the midline front area, not the side
- •C04.8 — Overlapping sites; use when tumor spans both anterior and lateral regions
- •C08.1 — Malignant neoplasm of sublingual gland; differentiate floor of mouth mucosal cancer from sublingual gland origin
- •C04.9 — Floor of mouth, unspecified; avoid when lateral location is documented