Ultrastructural, lectin histochemical and immunohistological observations on Merkel cell tumors.

The clinicopathological and ultrastructural findings of 10 cases of Merkel cell tumor (MCT) are presented. Three patients died rapidly due to tumor dissemination. The tumor cells in eight out of the 10 cases were positive for neuron-specific enolase, however, all were negative for the ten polypeptide hormones examined, as well as for the argentaffin and argyrophil reactions. One of the patients had suffered from chronic lymphocytic leukaemia. Particularly in this case, but also in the others, the differentiation of MCT from a malignant lymphoma necessitated immuno-histological, lectin histochemical and ultrastructural studies. The focal peanut agglutinin positivity of the tumor cells in 6 out of the 10 MCTs seems to be a characteristic feature of these cells.