C06.1
BillableMalignant neoplasm of vestibule of mouth
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C06.1 an HCC code?
Yes. C06.1 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 C06.1
For C06.1to 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 C06.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C06.1 is the ICD-10-CM diagnosis code for malignant neoplasm of vestibule of mouth. Cancer that starts in the vestibule of the mouth, which is the space between the lips/cheeks and the teeth. C06.1 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, C06.1 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, C06.1 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.
Verify documentation specifies the vestibule location to distinguish from other oral cavity sites. Because C06.1 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 C06.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies the vestibule location to distinguish from other oral cavity sites
- •Confirm histological type and laterality (left/right) when documented for more specific coding
Clinical Significance
Malignant neoplasm of the vestibule of mouth involves cancer in the narrow gutter-like space between the lips/cheeks and the teeth and gums. This location is clinically important because tumors here may involve multiple adjacent structures and can be difficult to assess on clinical examination alone.
Documentation Requirements
- ✓Pathology-confirmed malignancy with histological type
- ✓Specific documentation identifying the vestibule as the primary site
- ✓Upper vs lower vestibule specification if available
- ✓Laterality (left or right)
- ✓Assessment of involvement of adjacent gingiva, lip, or alveolar ridge
Commonly Confused Codes
- •C06.0 — Cheek mucosa; the vestibule is the groove between cheek/lip and gum, distinct from the broader cheek surface
- •C03.0/C03.1 — Malignant neoplasm of gum; tumors in the vestibule may extend to gingival tissue
- •C00.3-C00.5 — Lip, inner aspect; the vestibule borders the inner lip and these sites may overlap
- •C06.89 — Overlapping sites of mouth; use when tumor extends from vestibule to adjacent oral structures