Alphabetic Index FY2027

C04.0

Malignant neoplasm of anterior floor of mouth

FY2027Chapter 2: Neoplasms/C00–C14 Malignant neoplasms of lip, oral cavity and pharynx

BillableComplete code, valid to report
Care settingsHome Health Primary · MMTA - Infectious Disease, Neoplasms, and Blood-Forming DiseasesIPF Comorbidity · Oncology Treatment

C04.0 (also written C040) is a billable ICD-10-CM diagnosis code for malignant neoplasm of anterior floor of mouth. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 4 codes in category C04 (Malignant neoplasm of floor of mouth). Its coding notes include a Use additional code instruction.

Guidelines tip

From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.

A primary malignancy code stays in use until treatment directed at that site is completed. After that, with no evidence of disease at the site, Z85 gives the former site.

Guidelines I.C.2.mCurrent malignancy versus personal history of malignancyRead the official text

Use additional code

Add the listed code as a secondary code, if known.

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

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

Home Health Primary

Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Infectious Disease, Neoplasms, and Blood-Forming Diseases clinical group.

Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026

IPF Comorbidity

On the CMS IPF comorbidity list.

Comorbidity categoryFactor
Oncology Treatment1.44
It counts as a comorbidity when reported as a secondary diagnosis and actively treated during the stay. An IPF receives only one adjustment within a category and can receive adjustments in more than one category.

Source: CMS IPF PPS FY 2027 final rule (CMS-1847-F), Addendum B-3 (comorbidity codes with adjustment factor); effective for discharges on or after October 1, 2026

Inclusion terms

Conditions classified to this code.

This code
  • Malignant neoplasm of anterior to the premolar-canine junction

Notes

Also from chapter/block level (8 notes)
Inherited from Chapter 2 Neoplasms
  • Functional activity
  • All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
  • Morphology [Histology]
  • Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
  • Primary malignant neoplasms overlapping site boundaries
  • A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
  • Malignant neoplasm of ectopic tissue
  • Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).