MOC-31, Cytokeratin 7 and S-100 Protein Immunoreactivity in Merkel Cell and Merkel Cell Carcinoma

Abstract

The histological diagnosis of Merkel cell carcinoma can be difficult because it looks like other small blue cell tumors. In addition to the expected immunohistochemical results, some authors have reported reactivity for S-100 protein and CK 7 in Merkel cell carcinomas. The aim of the present work was to provide additional information about these unexpected immunoreactivities as well as to test the monoclonal antibody MOC-31 that was not previously described in Merkel cells or Merkel cell carcinomas. Nineteen cases of Merkel cell carcinoma were studied. MOC-31 plasma membrane immunoreactivity was found in 12 of 19 cases studied (63.1%). Immunoreactivity for CK 7 was observed in two cases (10.5%). S-100 protein was positive in four cases (21%). Normal human skin showed immunostaining for MOC-31 in the plasma membrane of virtually all Merkel cells. These cells were also immunoreactive for CK 7. S-100 protein was negative in human Merkel cells, but intensely positive in pig snout Merkel cells. In conclusion, normal human Merkel cells showed MOC-31 and CK 7 immunostaining and positivity for MOC-31, CK 7, and S-100 protein do not exclude the diagnosis of Merkel cell carcinoma.