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C04.1 ICD-10-CM Code: Malignant neoplasm of lateral floor of mouth

C04.1 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC04.1

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

C04.1

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

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.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of the lateral floor of mouth involves cancer of the side portions of the tissue beneath the tongue.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 21

Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 011

Code-level coefficient reference

ESRD/PACE

HCC 11

Code-level coefficient reference

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C04Malignant neoplasm of floor of mouthC04.1Malignant neoplasm of lateral floor of mouth

Inclusion Terms

Official

No inclusion terms are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Excludes 2

Official

No Excludes 2 notes are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Related Codes

Official
C04.0Malignant neoplasm of anterior floor of mouthC04.8Malignant neoplasm of overlapping sites of floor of mouthC04.9Malignant neoplasm of floor of mouth, unspecified

Includes

Official

No Includes notes are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Use Additional

Official
  • code to identify:Inherited from C04
  • alcohol abuse and dependence (F10.-)Inherited from C04
  • history of tobacco dependence (Z87.891)Inherited from C04
  • tobacco dependence (F17.-)Inherited from C04
  • tobacco use (Z72.0)Inherited from C04

Code Also

Official

No Code Also instructions are included in this display for C04.1. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
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)

MEAT Support

HCC Buddy guidance
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)

Audit Caution

HCC Buddy guidance
Using unspecified floor of mouth code (C04.9) when documentation clearly states lateral location
Confusing lateral floor of mouth with sublingual gland tumors (C08.1) when the cancer involves structures beneath the tongue
Failing to code extension to adjacent structures such as the mandible or tongue base
Not documenting laterality (left vs right) which is important for surgical planning and complete coding

Common Mistakes

HCC Buddy guidance
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

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 C04.1 an HCC code?

Yes. C04.1 (Malignant neoplasm of lateral floor of mouth) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C04.1 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
C04.1
Description
Malignant neoplasm of lateral floor of mouth
HCC (V28)
HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient
0.671
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers
0.671
ESRDHCC 11, Colorectal/Bladder/and Other Cancers
Not separately weighted
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C04.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C04.1

For C04.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • 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

Coder workflow notes

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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 source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C04.1; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Floor of mouth cancers often involve sublingual gland tissue. For C04.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, 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

Child Codes

C04.0Malignant neoplasm of anterior floor of mouth
HCC 21
C04.1Malignant neoplasm of lateral floor of mouth
HCC 21
C04.8Malignant neoplasm of overlapping sites of floor of mouth
HCC 21
C04.9Malignant neoplasm of floor of mouth, unspecified
HCC 21

Code Hierarchy

└C04Malignant neoplasm of floor of mouth└C04.1Malignant neoplasm of lateral floor of mouth
└C04.1Malignant neoplasm of lateral floor of mouth

Also searched as

  • C04 1
  • C041

For C04.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

C04.1 maps to CMS-HCC V28 category 21, Lymphoma and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C04.1. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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