Representative histology, immunohistochemistry and ISH of MCPyV-positive MCCs and -negative MCCs. MCPyV-positive MCC (A) showed immunoreactivity for CM2B4 (MCPyV-LT) (C), whereas MCPyV-negative MCC (B) was negative for CM2B4 (D). There were two MCPyV-ST positive patterns in MCPyV-positive MCCs; 1) Nuclear immunoreactivity for ST-1 (MCPyV-ST) (E-1) and 2) Nuclear and cytoplasmic immunostaining for ST-1 (E-2), whereas MCPyV-negative MCCs showed nuclear negativity and nonspecific cytoplasmic staining (F). Nuclear positivity for ISH (MCPyV-ST mRNA) was observed in MCPyV-positive MCCs (G), but no positive staining was detected in MCPyV-negative MCCs (H). A and B, H and E stain; A through H, original magnification × 400.