What is ICD-10 code C04.0?

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 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C04.0 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. C04.0 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. C04.0 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 C04.0?

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 C04.0, 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 C04.0?

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 Because C04.0 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 C04.0: Malignant neoplasm

ICD-10-CM Code View

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Code lookupC04.0Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C04.0

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

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.

Buddy Insight

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.

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

C04Malignant neoplasm of floor of mouth

C04.0Malignant neoplasm of anterior floor of mouth

Inclusion Terms

Official

Malignant neoplasm of anterior to the premolar-canine junction

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C04.0 in this effective period.

Related Child Codes

Official

C04.1Malignant neoplasm of lateral floor of mouth

C04.8Malignant neoplasm of overlapping sites of floor of mouth

C04.9Malignant neoplasm of floor of mouth, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C04.0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C04.0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C04.0 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 C04.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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

MEAT Support

HCC Buddy guidance

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

Audit Caution

HCC Buddy guidance

Confusing anterior floor of mouth with the ventral (under) surface of the tongue, which has its own code

Using C04.8 overlapping when the cancer is confined to the anterior region

Defaulting to C04.9 unspecified when operative or pathology reports specify the anterior location

Not capturing laterality or extension to adjacent structures that may require additional codes

Common Mistakes

HCC Buddy guidance

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

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 C04.0 an HCC code?

Yes. C04.0 (Malignant neoplasm of anterior floor 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: C04.0 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: C04.0
Description: Malignant neoplasm of anterior floor 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 C04.0 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C04.0

For C04.0 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 C04.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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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