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ICD-10-CM 2027 diagnosis code

C4AMerkel cell carcinoma

Not billable — use a more specific code

C4A is a header code, so it can't be reported by itself. Choose one of the 10 more specific codes beneath it.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About C4A

C4A is the ICD-10-CM diagnosis code for Merkel cell carcinoma. It belongs to block C43-C44 (melanoma and other malignant neoplasms of skin) and chapter 2 (neoplasms). It is a header code, so it can't be reported by itself; one of its 10 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: C4A.0 (of lip), C4A.1 (of eyelid, including canthus), C4A.2 (of ear and external auricular canal), C4A.3 (of other and unspecified parts of face), C4A.4 (of scalp and neck), C4A.5 (of trunk), C4A.6 (of upper limb, including shoulder), C4A.7 (of lower limb, including hip) and 2 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under C4A

Notes that apply from higher levels

Instructions written at a parent level also apply to C4A.

Broader instructions also apply from Chapter 2: Neoplasms.

Codes whose notes reference C4A

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about C4A

Is C4A billable?

No. C4A is a header code. Report one of its more specific subcodes instead.