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ICD-10 Code C4A.9: Merkel cell carcinoma, unspecified

C4A.9 is a billable ICD-10 diagnosis code used to classify Merkel cell carcinoma, unspecified in medical records and claims. You may see this code in hospital records, discharge summaries, insurance claims, encounter documentation, referrals, or other healthcare billing and coding records. ICD-10 codes are diagnosis classification codes used in healthcare records, reporting, coding workflows, and billing support. This code sits within the broader ICD-10 area for Neoplasms (C00-D49).

What is this code?

ICD-10 codes are diagnosis classification codes used in healthcare records, reporting, coding workflows, and billing support. This code sits within the broader ICD-10 area for Neoplasms (C00-D49).

When is it used?

  • May be used when a clinician documents merkel cell carcinoma, unspecified in a patient's medical record.
  • May appear in hospital records, claims, referrals, and clinical documentation.
  • This code can be used as a clinically usable diagnosis entry in standardized coding workflows.

What it does not mean

  • A code alone does not explain severity, treatment plan, or outcome.
  • A medical code should not be treated as a substitute for a doctor's diagnosis or advice.

Code hierarchy

chapter
2Neoplasms (C00-D49)
block
C00-C96Malignant neoplasms
block
C00-C75Malignant neoplasms, stated or presumed to be primary (of specified sites), and certain specified histologies, except neuroendocrine, and of lymphoid, hematopoietic and related tissue
block
C43-C44Melanoma and other malignant neoplasms of skin
category
C4AMerkel cell carcinoma
currentC4A

Official coding notes

Inclusion terms
  • Merkel cell carcinoma of unspecified site
  • Merkel cell carcinoma NOS

Where you may see this code

You may see this code in hospital records, discharge summaries, insurance claims, encounter documentation, referrals, or other healthcare billing and coding records.

Related specialists

OncologistGeneral Physician

Coverage-related procedures and services

CPT 81479high
UNLISTED MOLECULAR PATHOLOGY PROCEDURE
Source: CMS coverage guidance
CPT 81445high
SOLID ORGAN NEOPLASM, GENOMIC SEQUENCE ANALYSIS PANEL, 5-50 GENES, INTERROGATION FOR SEQUENCE VARIANTS AND COPY NUMBER VARIANTS OR REARRANGEMENTS, IF PERFORMED; DNA ANALYSIS OR COMBINED DNA AND RNA ANALYSIS
Source: CMS coverage guidance
CPT 0543Uhigh
ONCOLOGY (SOLID TUMOR), NEXT-GENERATION SEQUENCING OF DNA FROM FORMALIN-FIXED PARAFFIN-EMBEDDED (FFPE) TISSUE OF 517 GENES, INTERROGATION FOR SINGLE-NUCLEOTIDE VARIANTS, MULTI-NUCLEOTIDE VARIANTS, INSERTIONS AND DELETIONS FROM DNA, FUSIONS IN 24 GENES AND SPLICE VARIANTS IN 1 GENE FROM RNA, AND TUMOR MUTATION BURDEN
Source: CMS coverage guidance
CPT 0329Uhigh
ONCOLOGY (NEOPLASIA), EXOME AND TRANSCRIPTOME SEQUENCE ANALYSIS FOR SEQUENCE VARIANTS, GENE COPY NUMBER AMPLIFICATIONS AND DELETIONS, GENE REARRANGEMENTS, MICROSATELLITE INSTABILITY AND TUMOR MUTATIONAL BURDEN UTILIZING DNA AND RNA FROM TUMOR WITH DNA FROM NORMAL BLOOD OR SALIVA FOR SUBTRACTION, REPORT OF CLINICALLY SIGNIFICANT MUTATION(S) WITH THERAPY ASSOCIATIONS
Source: CMS coverage guidance
CPT 0340Uhigh
ONCOLOGY (PAN-CANCER), ANALYSIS OF MINIMAL RESIDUAL DISEASE (MRD) FROM PLASMA, WITH ASSAYS PERSONALIZED TO EACH PATIENT BASED ON PRIOR NEXT-GENERATION SEQUENCING OF THE PATIENT'S TUMOR AND GERMLINE DNA, REPORTED AS ABSENCE OR PRESENCE OF MRD, WITH DISEASE-BURDEN CORRELATION, IF APPROPRIATE
Source: CMS coverage guidance
CPT 0422Uhigh
ONCOLOGY (PAN-SOLID TUMOR), ANALYSIS OF DNA BIOMARKER RESPONSE TO ANTI-CANCER THERAPY USING CELL-FREE CIRCULATING DNA, BIOMARKER COMPARISON TO A PREVIOUS BASELINE PRE-TREATMENT CELL-FREE CIRCULATING DNA ANALYSIS USING NEXT-GENERATION SEQUENCING, ALGORITHM REPORTED AS A QUANTITATIVE CHANGE FROM BASELINE, INCLUDING SPECIFIC ALTERATIONS, IF APPROPRIATE
Source: CMS coverage guidance

Coding guidelines

Common synonyms

Merkel cell carcinoma, unspecifiedMerkel cell carcinoma

Frequently asked questions

Code details

CodeC4A.9
SystemICD10
Display nameMerkel cell carcinoma, unspecified
ChapterNeoplasms (C00-D49)
BlockMelanoma and other malignant neoplasms of skin

Flags

BillableYes
Valid clinical useYes

Source

SourceICD-10
Version2026-annual
Releaseannual
Year2026

Index terms

Matched terms
Carcinoma(malignant)

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.