C04.9
BillableMalignant neoplasm of floor of mouth, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C04.9 an HCC code?
Yes. C04.9 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors 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 C04.9
For C04.9 to 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 C04.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C04.9 is the ICD-10-CM diagnosis code for malignant neoplasm of floor of mouth, unspecified. Cancer of the floor of mouth when the specific location or extent within that region is not documented. C04.9 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, C04.9 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C04.9 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.306. 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 only when specific floor of mouth location cannot be determined. Because C04.9 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 C04.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use only when specific floor of mouth location cannot be determined
- •Query provider for more specific anatomical location if available
Clinical Significance
This unspecified floor of mouth cancer code indicates documentation lacks anatomical detail about which portion of the floor of mouth is involved. While it captures the same HCC, this code may trigger audit scrutiny and represents suboptimal documentation quality.
Documentation Requirements
- ✓Pathology confirmation of malignancy in the floor of mouth
- ✓Evidence that a provider query was attempted to determine anterior vs lateral location
- ✓Staging information and current treatment plan
- ✓Documentation explaining why more specific location cannot be determined
- ✓Review of all available imaging and surgical reports for additional location detail
Commonly Confused Codes
- •C04.0 — Anterior floor of mouth; use when documentation specifies anterior location
- •C04.1 — Lateral floor of mouth; use when documentation specifies lateral or side location
- •C04.8 — Overlapping sites of floor of mouth; use when tumor spans multiple regions
- •C06.9 — Malignant neoplasm of mouth, unspecified; even less specific — at least C04.9 confirms floor of mouth