2026 ICD-10-CM Diagnosis Code C4AMerkel cell carcinoma

ICD-10-CM Codes›C00–D49›C43-C44›C4A

ICD-10-CM C4A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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

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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C4AOverview

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.