2027 ICD-10-CM Diagnosis Code C4AMerkel cell carcinoma

ICD-10-CM Codes›C00–D49›C43-C44›C4A

ICD-10-CM C4A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

C4A is a non-billable ICD-10-CM category code for merkel cell carcinoma, so it cannot be submitted on claims. Use a more specific code from this category instead, such as C4A.0, C4A.10, C4A.111, and C4A.112.

Code Identity

ICD-10-CM Code
C4A
Billable Status
No — Non-Billable Category
Code Describes
Merkel cell carcinoma
Short Description
Merkel cell carcinoma
Same as the full description in the CMS dataset.
Chapter
C43-C44
Melanoma and other malignant neoplasms of skin

Code Classification

ChapterC00–D49Neoplasms
SectionC43-C44Melanoma and other malignant neoplasms of skin
CategoryC4AMerkel cell carcinoma
This CodeC4AMerkel cell carcinoma

Specific Coding for Merkel cell carcinomaOverview

Non-specific codes like C4A require more characters. Use one of these billable codes instead:

  • Use C4A.0 for Merkel cell carcinoma of lip

  • C4A.1 for Merkel cell carcinoma of eyelid, including canthus

  • Use C4A.10 for Merkel cell carcinoma of unspecified eyelid, including canthus

  • C4A.11 for Merkel cell carcinoma of right eyelid, including canthus

  • C4A.12 for Merkel cell carcinoma of left eyelid, including canthus

  • C4A.2 for Merkel cell carcinoma of ear and external auricular canal

  • Use C4A.20 for Merkel cell carcinoma of unspecified ear and external auricular canal

  • Use C4A.21 for Merkel cell carcinoma of right ear and external auricular canal

  • Use C4A.22 for Merkel cell carcinoma of left ear and external auricular canal

  • C4A.3 for Merkel cell carcinoma of other and unspecified parts of face

  • Use C4A.30 for Merkel cell carcinoma of unspecified part of face

  • Use C4A.31 for Merkel cell carcinoma of nose

  • Use C4A.39 for Merkel cell carcinoma of other parts of face

  • Use C4A.4 for Merkel cell carcinoma of scalp and neck

  • C4A.5 for Merkel cell carcinoma of trunk

  • Use C4A.51 for Merkel cell carcinoma of anal skin

  • Use C4A.52 for Merkel cell carcinoma of skin of breast

  • Use C4A.59 for Merkel cell carcinoma of other part of trunk

  • C4A.6 for Merkel cell carcinoma of upper limb, including shoulder

  • Use C4A.60 for Merkel cell carcinoma of unspecified upper limb, including shoulder

  • Use C4A.61 for Merkel cell carcinoma of right upper limb, including shoulder

  • Use C4A.62 for Merkel cell carcinoma of left upper limb, including shoulder

  • C4A.7 for Merkel cell carcinoma of lower limb, including hip

  • Use C4A.70 for Merkel cell carcinoma of unspecified lower limb, including hip

  • Use C4A.71 for Merkel cell carcinoma of right lower limb, including hip

  • Use C4A.72 for Merkel cell carcinoma of left lower limb, including hip

  • Use C4A.8 for Merkel cell carcinoma of overlapping sites

  • Use C4A.9 for Merkel cell carcinoma, unspecified

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to C4A: its own notes plus those printed at Chapter 2. A note printed at a category, block or chapter applies to every code under it.

Notes

General instructions on how these codes are used.

From Chapter 2 (C00-D49) Neoplasms applies to 1,730 codes
  • 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).

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name C4A, its category, or a range that includes it.

Applicable To 1

These notes mention C4A.

  • Z85.821 Personal history of Merkel cell carcinoma
    Conditions classifiable to C4A

Excludes1 1

These codes carry an Excludes1 note naming C4A: they are not reported together with it, unless the two conditions are unrelated.

  • C44 Other and unspecified malignant neoplasm of skin
    Merkel cell carcinoma (C4A.-)

Excludes2 2

These codes carry an Excludes2 note naming C4A: its condition is not part of those codes, and both may be reported when the patient has both.

  • C43 Malignant melanoma of skin
    Merkel cell carcinoma (C4A.-)
  • C7A Malignant neuroendocrine tumors
    Merkel cell carcinoma (C4A.-)

Clinical InformationClinical

  • Carcinoma, Merkel Cell

    a carcinoma arising from merkel cells located in the basal layer of the epidermis and occurring most commonly as a primary neuroendocrine carcinoma of the skin. merkel cells are tactile cells of neuroectodermal origin and histologically show neurosecretory granules. the skin of the head and neck are a common site of merkel cell carcinoma, occurring generally in elderly patients. (holland et al., cancer medicine, 3d ed, p1245)

Patient EducationClinical

Skin Cancer

Skin cancer is the most common form of cancer in the United States. The two most common types are basal cell cancer and squamous cell cancer. They usually form on the head, face, neck, hands, and arms. Another type of skin cancer, melanoma, is more dangerous but less common.

Read the full article at MedlinePlus

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

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About C4AOverview

What is the ICD-10 code for merkel cell carcinoma?

C4A is the ICD-10-CM category for merkel cell carcinoma, but it is a non-billable header: claims need a more specific code from this category, listed on this page.

Is C4A (Merkel cell carcinoma) a billable code?

No. This is a category header that groups the codes for merkel cell carcinoma, and headers cannot be submitted on claims. Claims for merkel cell carcinoma need a more specific code from this category, such as C4A.0, C4A.10, and C4A.111.