ICD-10-CM Tabular Index · Chapter 2 · FY 2027 C4A

Merkel cell carcinoma (C4A) ICD-10-CM

The C4A code range covers merkel cell carcinoma with 33 ICD-10-CM diagnosis codes. 24 of them are billable and valid for claim submission in fiscal year 2027, and the category headers group them but cannot themselves be billed.

✓ Built from the official CMS FY 2027 datasetEffective Oct 1, 2026 – Sep 30, 2027
33
Diagnosis Codes
24
Billable Codes
C4A
Code Range
C43–C44
Parent Section
ICD-10-CM

Codes in the C4A Range 33 codes · 24 billable

33 of 33 shown
  • C4A Merkel cell carcinomaNon-billable
  • C4A.0 Merkel cell carcinoma of lip
  • C4A.1 Merkel cell carcinoma of eyelid, including canthusNon-billable
  • C4A.10 Merkel cell carcinoma of unspecified eyelid, including canthus
  • C4A.11 Merkel cell carcinoma of right eyelid, including canthusNon-billable
  • C4A.111 Merkel cell carcinoma of right upper eyelid, including canthus
  • C4A.112 Merkel cell carcinoma of right lower eyelid, including canthus
  • C4A.12 Merkel cell carcinoma of left eyelid, including canthusNon-billable
  • C4A.121 Merkel cell carcinoma of left upper eyelid, including canthus
  • C4A.122 Merkel cell carcinoma of left lower eyelid, including canthus
  • C4A.2 Merkel cell carcinoma of ear and external auricular canalNon-billable
  • C4A.20 Merkel cell carcinoma of unspecified ear and external auricular canal
  • C4A.21 Merkel cell carcinoma of right ear and external auricular canal
  • C4A.22 Merkel cell carcinoma of left ear and external auricular canal
  • C4A.3 Merkel cell carcinoma of other and unspecified parts of faceNon-billable
  • C4A.30 Merkel cell carcinoma of unspecified part of face
  • C4A.31 Merkel cell carcinoma of nose
  • C4A.39 Merkel cell carcinoma of other parts of face
  • C4A.4 Merkel cell carcinoma of scalp and neck
  • C4A.5 Merkel cell carcinoma of trunkNon-billable
  • C4A.51 Merkel cell carcinoma of anal skin
  • C4A.52 Merkel cell carcinoma of skin of breast
  • C4A.59 Merkel cell carcinoma of other part of trunk
  • C4A.6 Merkel cell carcinoma of upper limb, including shoulderNon-billable
  • C4A.60 Merkel cell carcinoma of unspecified upper limb, including shoulder
  • C4A.61 Merkel cell carcinoma of right upper limb, including shoulder
  • C4A.62 Merkel cell carcinoma of left upper limb, including shoulder
  • C4A.7 Merkel cell carcinoma of lower limb, including hipNon-billable
  • C4A.70 Merkel cell carcinoma of unspecified lower limb, including hip
  • C4A.71 Merkel cell carcinoma of right lower limb, including hip
  • C4A.72 Merkel cell carcinoma of left lower limb, including hip
  • C4A.8 Merkel cell carcinoma of overlapping sites
  • C4A.9 Merkel cell carcinoma, unspecified

Clinical Terms in This Code Range

Definitions from the National Library of Medicine for conditions coded in the C4A range.

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)

About the C4A Code Range

Merkel cell carcinoma is a cancer that starts in Merkel cells at the base of the skin’s outer layer.

The codes group it by site: the lip, eyelid, ear, face, scalp and neck, trunk, or limbs. Eyelid codes distinguish right from left and upper from lower. Ear and limb codes distinguish right from left. Face codes separate the nose from other or unspecified parts; trunk codes separate anal skin, breast skin, and other parts. C4A.8 identifies overlapping sites, while C4A.9 leaves the site unspecified.

Questions About This Page

How many billable codes are in the C4A range?

Of the 33 codes in this range, 24 are billable and valid for claim submission from October 1, 2026 through September 30, 2027. Category header codes group them but cannot be reported on claims.

What does the C4A range classify?

The range classifies merkel cell carcinoma. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.

Related References

All ICD-10-CM ChaptersAll of Chapter 2ICD-10-CM Code LookupMS-DRG ReferenceMedicare Code EditsPOA Exempt Codes

Source: CMS FY 2027 ICD-10-CM Tabular List and order file, effective October 1, 2026 through September 30, 2027.