Merkel cell carcinoma of overlapping sites

This code represents Merkel cell carcinoma (MCC) that involves multiple contiguous or overlapping anatomical sites, making it impossible to assign to a single primary site. MCC is a rare, aggressive neuroendocrine tumor of the skin, often presenting as a rapidly growing, firm, painless nodule.

Use this code when documentation clearly indicates Merkel cell carcinoma affecting multiple adjacent body regions, such as a tumor spanning the neck and face, or the trunk and an extremity. This code is appropriate when the physician explicitly states "overlapping sites" or provides a detailed description that precludes a more specific site assignment.

• Ensure the documentation explicitly states or clearly implies involvement of multiple contiguous sites for the Merkel cell carcinoma.
• Do not use this code if the primary site can be clearly identified, even if there are metastases. This code is for the primary tumor's location.
• Always sequence this code as the primary diagnosis when it represents the reason for the encounter.