2026 ICD-10-CM Diagnosis Code C04.1Malignant neoplasm of lateral floor of mouth

ICD-10-CM Codes›C00–D49›C00-C14›C04

ICD-10-CM C04.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C04.1 is a billable ICD-10-CM diagnosis code for malignant neoplasm of lateral floor of mouth. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 146 through 148. Coders also document this condition as carcinoma of lateral part of floor of mouth. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Head and neck cancers - lip and oral cavity.

Code Identity

ICD-10-CM Code
C04.1
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of lateral floor of mouth
Short Description
Malignant neoplasm of lateral floor of mouth
Same as the full description in the CMS dataset.
Parent Code
C04
Malignant neoplasm of floor of mouth

Code Classification

ChapterC00–D49Neoplasms
SectionC00-C14Malignant neoplasms of lip, oral cavity and pharynx
CategoryC04Malignant neoplasm of floor of mouth
This CodeC04.1Malignant neoplasm of lateral floor of mouth

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Carcinoma of lateral part of floor of mouth
  • Malignant neoplasm of anterior and lateral floor of mouth
  • Malignant neoplasm of anterior floor of mouth
  • Malignant neoplasm of lateral floor of mouth
  • Primary carcinoma of lateral part of floor of mouth
  • Primary malignant neoplasm of lateral portion of floor of mouth
  • Primary squamous cell carcinoma of lateral floor of mouth

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO002
Head and neck cancers - lip and oral cavity
Default principal diagnosis: inpatient Yes · outpatient Yes

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
mouth › floor › lateral portionC04.1C79.89D00.06D10.2D37.09D49.0

Patient EducationClinical

Oral Cancer

Oral cancer is cancer of the mouth. It is a type of head and neck cancer. Most oral cancers are squamous cell cancers. They begin in the flat cells that cover the surfaces of your mouth, tongue, and lips. The cancer cells may spread into deeper tissue as the cancer grows.

The full article covers:

  • What is oral cancer?
  • Who is more likely to develop oral cancer?
  • What are the symptoms of oral cancer?
  • How is oral cancer diagnosed?
  • What are the treatments for oral cancer?
  • Can oral cancer be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert C04.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
144.1 Mal neo lat floor mouth
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C04.1Overview

Is C04.1 (Malignant neoplasm of floor of mouth) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of lateral floor of mouth on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C04.1 group to?

When malignant neoplasm of lateral floor of mouth is the principal diagnosis on an inpatient stay, it groups to MS-DRG 146, 147, 148, with relative weights from 0.7971 to 2.1174 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C04.1?

Under the General Equivalence Mappings, malignant neoplasm of lateral floor of mouth converts to ICD-9-CM 144.1 (mal neo lat floor mouth). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.