Table 3.
Distinct features of MCPyV-positive and -negative MCC cases.
| Features | MCPyV(+) Merkel cell carcinoma | MCPyV(–) Merkel cell carcinoma |
|---|---|---|
| MORPHOLOGY | ||
| Nucleus | Round (110, 111) | Irregular/spindle (110, 111) |
| Cytoplasm | Few (110, 111) | More abundant (110, 111) |
| Divergent differentiation | No (103, 104) | Yes (103, 104) |
| IMMUNOHISTOCHEMICAL MARKERS | ||
| CK20 | +(112, 113) | +/–(112, 113) |
| CK7 | –(112) | +/–(112) |
| TTF1 | –(112, 114) | +/–(112, 114) |
| Neurofilament | +(14, 106, 112) | +/–(14, 106, 112) |
| Oncogenic triggers | MCPyV T antigens (16, 68, 79, 115) |
UV induced genetic alteration (22, 116, 117) |
| Mutation load | Low (22, 116, 117) | High (22, 116, 117) |
(+), frequent positivity of the marker; (–), frequent negativity of the marker; (+/–) increased or decrease expression frequency of this marker compared to the MCPyV(+) subset.
Compared to the MCPyV-positive MCC cells MCPyV-negative MCC tumor cells have been described to harbor more irregular nuclei, more abundant cytoplasm and display more frequently so called divergent differentiation. Moreover, MCPyV-negative cases are characterized by an specific immunohistochemical profile with frequent lack of expression of CK20 and neurofilaments, and more frequent positivity for TTF1 and CK7. Finally, very high mutational burden with UV signature are observed only in MCPyV-negative cases.