What is ICD-10 code C06.1?

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. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C06.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C06.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C06.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C06.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C06.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C06.1, V28 maps to Lymphoma and Other Cancers at RAF 0.671 while V24 mapped to Colorectal, Bladder, and Other Cancers at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C06.1?

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 Because C06.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM C06.1: Malignant neoplasm

ICD-10-CM Code View

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Code lookupC06.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lip, oral cavity and pharynx (C00-C14)

C06.1

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy Insight

Malignant neoplasm of the vestibule of mouth involves cancer in the narrow gutter-like space between the lips/cheeks and the teeth and gums.

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

RAF 0.671

CMS-HCC V24

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.307

ACA/HHS

Mapped

HCC 11

HHS-HCC 11

Varies by metal level

ESRD/PACE

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.059

RXHCC

Mapped

HCC 22

Cancer, Other Specified Sites

RAF 0.124

Code Book Path

Official

C06Malignant neoplasm of other and unspecified parts of mouth

C06.1Malignant neoplasm of vestibule of mouth

Inclusion Terms

Official

Malignant neoplasm of buccal sulcus (upper) (lower)
Malignant neoplasm of labial sulcus (upper) (lower)

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C06.1 in this effective period.

Related Child Codes

Official

C06.0Malignant neoplasm of cheek mucosa

C06.2Malignant neoplasm of retromolar area

C06.8Malignant neoplasm of overlapping sites of other and unspecified parts of mouth

C06.9Malignant neoplasm of mouth, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C06.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C06.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C06.1 in this effective period.

Use Additional

Official

code to identify:
alcohol abuse and dependence (F10.-)
history of tobacco dependence (Z87.891)
tobacco dependence (F17.-)
tobacco use (Z72.0)

Code Also

Official

ICD-10-CM does not list Code Also instructions for C06.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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)

MEAT Support

HCC Buddy guidance

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)

Audit Caution

HCC Buddy guidance

Confusing vestibule of mouth with cheek mucosa — the vestibule is the sulcus (groove) between the inner lip/cheek and the alveolar ridge

Not querying the provider about whether the tumor extends to gingiva or lip, which would change the code selection

Failing to document upper vs lower vestibule for more complete clinical picture

Using this code for benign conditions of the vestibule rather than confirmed malignancy

Common Mistakes

HCC Buddy guidance

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

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C06.1 an HCC code?

Yes. C06.1 (Malignant neoplasm of vestibule of mouth) maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24), with a community non-dual aged RAF of 0.671. It is billable for payment year 2026.

Coder answer: C06.1 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C06.1
Description: Malignant neoplasm of vestibule of mouth
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

V24HCC 11, Colorectal, Bladder, and Other Cancers

0.307

ESRDHCC 11, Colorectal, Bladder, and Other Cancers

0.059

RxHCCHCC 22, Cancer, Other Specified Sites

0.124

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. 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.

Work C06.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C06.1

For C06.1 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 C06.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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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