Figure 1

Merkel cell carcinoma (MCC) xenograft model. NSG mice injected with human MCC lines (WaGa, top panels; MKL-1, bottom panels) developed visible tumor masses (encircled in dotted lines) within a month (left panels; original magnification, × 1) of tumor cell xenografting. Tumors involved the dermis and the subcutaneous tissue and were composed of uniform, small basophilic cells (center panels; original magnification, × 100). The classic salt and pepper chromatin pattern was observed within rounded nuclei rimmed by scant cytoplasm that showed dot-like positivity for cytokeratin 20 (CK20; right panels; original magnification × 1000).