These tumors have a tendency to grow rapidly. This narrows the differential diagnosis. In patients with rapid growth the most common neoplastic diagnosis are lymphoma, Merkel cell tumor and giant keratoacanthoma. Biopsy is mandatory. Regional metastases present as enlarged, firm, painless lymph nodes.
Systemic disease presents most often as masses in the skin, lungs, liver, bone, and brain.
Just over 600 cases have been reported worldwide. The tumor is rare in individuals who are not Caucasian. MCC affects males and females equally. However, reports of MCC uncommonly occurring in unexposed sites, such as the genitalia or oral mucosa, suggests that other factors must play a role. The histopathologic features of MCC on light microscopy are distinctive but not specific.