C4A.51 Merkel cell carcinoma of anal skin

Billable ICD-10-CM code, FY2026.

Applicable to

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

Applies from C4A.5 Merkel cell carcinoma of trunk

Excludes2 (not included here)

• malignant neoplasm of anus NOS (C21.0)
• malignant neoplasm of scrotum (C63.2)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 21 — Lymphoma and Other Cancers
• CMS-HCC V22: HCC 12 — Breast, Prostate, and Other Cancers and Tumors
• RxHCC V08: HCC 22 — Prostate, Breast, Bladder, and Other Cancers and Tumors
• ESRD V24: HCC 12

MS-DRG index

Defines the logic of DRG(s) 595-596 in MDC 09.

Approximate ICD-9-CM (GEMs)

• 209.35 Merkel cell carcinoma of the trunk (approximate)

Code annotations containing back-references to C4A.51

Back-references to C4A

• Type 2 Excludes: C43 Malignant melanoma of skin ("Merkel cell carcinoma (C4A.-)")
• Type 1 Excludes: C44 Other and unspecified malignant neoplasm of skin ("Merkel cell carcinoma (C4A.-)")
• Type 2 Excludes: C7A Malignant neuroendocrine tumors ("Merkel cell carcinoma (C4A.-)")

Diagnosis Index entries for C4A.51

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

Nearby codes

• 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 trunk
• C4A.51 Merkel cell carcinoma of anal skin (this code)
• 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 shoulder
• C4A.60 Merkel cell carcinoma of unspecified upper limb, including shoulder
• C4A.61 Merkel cell carcinoma of right upper limb, including shoulder