A study of apoptosis in Merkel cell carcinoma - An immunohistochemical, ultrastructural, DNA ladder, and TUNEL labeling study

We performed immunohistochemical, ultrastructural, terminal deoxynucleotidy l transferase-mediated dUTP-biotin nick-end labeling (TUNEL), and DNA ladde r studies of apoptosis in nine cases of Merkel cell carcinoma (MCC). None o f the cases showed spontaneous regression as has been reported in several M CCs. Neuron-specific enolase was demonstrated by immunohistochemistry (8/8 MCCs), and staining for cytokeratin 20 was positive (2/8 MCCs). Ultrastruct ural examination revealed many cytoplasmic dense-cored granules, desmosome- like structures, and intermediate filaments. The granules were seen along t he plasma membrane or around perinuclear centrioles. We found various stage s of development of apoptotic bodies. Apoptosis resulted in vacuolization a nd fragmentation of nuclei and phagocytosed bodies in tumor cells. Apoptoti c cells were also detected by TUNEL, DNA ladder, and immunostaining using t he antibody against Fas (Apo-1/CD95) antigen. It seems that a high apoptoti c rate is a common finding in MCC, although spontaneous regression is an ex ceedingly rare event. It is thus unlikely that apoptosis alone would explai n spontaneous regression.