[Merkel cell carcinoma of the skin. Anatomoclinical, ultrastructural and immunohistochemical study of 14 cases].

The clinical and pathological features of 14 cases of Merkel cell carcinoma are reported. They commonly arise in the skin of elderly patients, particularly on the face and pelvis. They have a loco-regional aggressivity (nodal metastases in 4 cases) but some patients die with disseminated metastases (2 cases). These tumors are composed of round cells with scanty cytoplasm, arranged in solid or trabecular sheets. Mitotic figures are usually numerous. The ultrastructural study reveal secretory granules and paranuclear collection of intermediate filaments. Immunohistochemical phenotype is highly characteristic: cytoplasmic diffuse positivity with an anti-neuron-specific enolase polyclonal antibody; polar and/or diffuse positivity with anti-cytokeratin, anti-epithelial membrane antigen and anti-S100 protein monoclonal antibodies; polar positivity with an anti-neurofilament monoclonal antibody. The negativity with an anti-common leucocyte antigen monoclonal antibody is helpful to differentiate Merkel cell carcinoma from cutaneous malignant lymphoma.