2026 ICD-10-CM Diagnosis Code C4A.22Merkel cell carcinoma of left ear and external auricular canal

ICD-10-CM Codes›C00–D49›C43-C44›C4A

ICD-10-CM C4A.22
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C4A.22 is a billable ICD-10-CM diagnosis code for merkel cell carcinoma of left ear and external auricular canal. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 595 through 596. Coders also document this condition as primary malignant neoplasm of skin of ear. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Skin cancers - all other types.

Code Identity

ICD-10-CM Code
C4A.22
Billable Status
Yes — Valid for Submission
Code Describes
Merkel cell carcinoma of left ear and external auricular canal
Short Description
Merkel cell carcinoma of left ear and external auric canal
Parent Code
C4A.2
Merkel cell carcinoma of ear and external auricular canal

Code Classification

ChapterC00–D49Neoplasms
SectionC43-C44Melanoma and other malignant neoplasms of skin
CategoryC4AMerkel cell carcinoma
This CodeC4A.22Merkel cell carcinoma of left ear and external auricular canal

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Primary malignant neoplasm of skin of ear
  • Primary malignant neoplasm of skin of left ear
  • Primary Merkel cell carcinoma of skin of ear
  • Primary Merkel cell carcinoma of skin of left ear

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO028
Skin cancers - all other types
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

Convert C4A.22 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
209.31 Merkel cell ca-face
Approximate The match is approximate rather than exact.

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 C4A.22Overview

Is C4A.22 (Merkel cell carcinoma of ear and external auricular canal) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report merkel cell carcinoma of left ear and external auricular canal on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C4A.22 group to?

When merkel cell carcinoma of left ear and external auricular canal is the principal diagnosis on an inpatient stay, it groups to MS-DRG 595, 596, with relative weights from 1.0825 to 2.1207 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C4A.22?

Under the General Equivalence Mappings, merkel cell carcinoma of left ear and external auricular canal converts to ICD-9-CM 209.31 (merkel cell ca-face). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.