Merkel cell carcinoma of anal skin

This code identifies a rare and aggressive neuroendocrine carcinoma, Merkel cell carcinoma, specifically originating in the skin of the anal region. It is characterized by rapid growth and a high propensity for local recurrence and distant metastasis.

Apply this code when documentation confirms a pathological diagnosis of Merkel cell carcinoma located on the anal skin. This diagnosis is typically established via biopsy and immunohistochemical staining. It is used for primary tumors in this specific anatomical site.

• Ensure the documentation explicitly states "anal skin" to differentiate from perianal or rectal involvement.
• Do not confuse with squamous cell carcinoma or melanoma of the anal skin; these have distinct codes.
• Sequence this code as the primary diagnosis when it is the reason for the encounter, followed by any relevant secondary diagnoses such as metastatic disease.