Table 1.
Characteristics of Merkel cell polyomavirus+ and Merkel cell polyomavirus- Merkel cell carcinomas
| Feature | MCPyV+ | MCPyV− |
|---|---|---|
| Gender | Female > male | Male > female |
| Anatomic distribution | Limbs>Head and neck | Head and neck > limbs |
| Geographic distribution | US and Europe (+++)a | Australia (+++) |
| Morphology | Pure | Pure and combined |
| IHC | Classicalb | Classical or aberrant |
| Immune response | TILS (+++) | TILS (+) |
| Prognosis | Better | Worse |
| Response to ICI | Favorable | Favorable |
| Genetics | Mutational burden-low | Mutational burden-high |
| Rec mut RB1 and TP53-absent | Rec mut RB1 and TP53-present | |
| UV mut sign-absent | UV mut sig-present |
aThe designation (+++), (as opposed to [+]) is used to semi-quantitatively represent frequency of occurrence, bThe classical pattern of IHC is CK20+, synaptophysin+. MCPyV+, neurofilament +, CK7−and TTF-1. Variations on this pattern are considered aberrant. MCPyV: Merkel cell polyomavirus, IHC: Immunohistochemistry, TILS: Tumor infiltrating lymphocytes, ICI: Immune checkpoint inhibition, RB: Retinoblastoma, TTF: Thyroid transcription factor, CK: Cytokeratin