C4A.51 Merkel cell carcinoma of anal skin

The ICD-10-CM code for Merkel cell carcinoma of anal skin is C4A.51 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

2: Neoplasms (C00-D49)

Section

C43-C44: Melanoma and other malignant neoplasms of skin (C43-C44)

Category C4A

33 codes (24 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to C4A.51:

• Carcinoma (malignant) › Merkel cell › anal margin
• Carcinoma (malignant) › Merkel cell › anal skin
• Carcinoma (malignant) › Merkel cell › perianal skin

Inclusion Terms

• Merkel cell carcinoma of anal margin
• Merkel cell carcinoma of perianal skin

U.S. Hospital Utilization

C4A.51 appeared in too few sampled U.S. inpatient stays in 2022 to report a national estimate (AHRQ suppresses counts of 10 or fewer) — a rare inpatient diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)