Merkel cell carcinoma. Histopathology, immunohistochemistry, and cytogenetic analysis.

BACKGROUND

Merkel cell carcinoma (MCC) is a cutaneous neoplasm, histopathologically difficult to differentiate from other small blue cell neoplasms. Immunohistochemical and ultrastructural analyses are usually helpful in differentiating these neoplasms. Recently, cytogenetic analysis has emerged as a potential tool in the diagnosis of solid neoplasms, including MCC.

OBJECTIVE

To describe the immunohistochemical and cytogenetic features of a case of primary MCC and to review the cytogenetics literature on MCC.

METHODS

Formalin-fixed tissue was processed routinely and labeled with a battery of antibodies. Metaphase cells from fresh tissue were prepared by Giemsa banding.

RESULTS

Histopathologically, there were irregular aggregates of pyknotic cells with little cytoplasm. Immunohistochemically, the neoplastic cells stained positive for neurofilament, cytokeratin, neuron-specific enolase, and epithelial membrane antigen. Leucocyte common antigen, S-100, 013, and chromogranin were negative. Karyotyping of neoplastic cells showed loss of chromosome Y (-Y).

CONCLUSIONS

Coexpression of cytokeratin and neurofilament is characteristic of MCC and allows it to be differentiated from similar neoplasms. The significance of Y chromosome loss is unclear. Further cytogenetic analyses are warranted to identify genetic mutations significant to the pathogenesis of MCC.