Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine cutaneous tumor with a high mortality rate. 1 Evidence supports 2 molecular subclasses of MCC: virus-positive MCC associated with oncogenic Merkel cell polyomavirus (MCPyV), and virus-negative MCC (VN-MCC) associated with UV signature mutations. 1, 2, 3 Typically, MCC presents as a pink papule or nodule on sun-exposed skin of white, elderly individuals. 1 MCC most frequently presents in the head and neck area, followed by the upper extremities. 1 MCC commonly metastasizes to regional lymph nodes and skin, with potential for distant metastases to skin, lung, liver, central nervous system, and bone. 3 Patients may have a high burden of satellite and in-transit cutaneous metastases, which may be histologically identical to primary MCC tumors. 1, 3

In approximately 1% to 2% of patients with MCC, a second MCC tumor will arise that is clinically compatible with a new primary MCC. 1, 4 In such cases, molecular analyses may be useful in distinguishing a second primary MCC tumor from a distant cutaneous metastasis. 4, 5, 6, 7, 8