Secondary Merkel cell carcinoma

This code signifies the presence of Merkel cell carcinoma that has metastasized from a primary site to a secondary location in the body. It indicates that the tumor found is not the original cancer but rather a spread from an existing Merkel cell carcinoma.

Use this code when documentation clearly states secondary Merkel cell carcinoma, often identified through biopsy of a metastatic lesion. This code is appropriate for patients undergoing treatment or surveillance for metastatic disease originating from a previously diagnosed Merkel cell carcinoma.

• Always sequence the primary Merkel cell carcinoma code (e.g., C4A.-) before this secondary code, if the primary site is still active or being treated.
• Ensure the documentation explicitly states "secondary" or "metastatic" Merkel cell carcinoma, rather than just "Merkel cell carcinoma" in a new location.
• Do not use this code for primary Merkel cell carcinoma, even if it is a new primary tumor.