What special stains are available to diagnose MCC?

MCC often has a characteristic paranuclear “dot” that stains with cytokeratin, especially cytokeratin 20. MCC also stains positively for various neuroendocrine markers, such as synaptophysin, chromogranin A, neuron-specific enolase, calcitonin, and vasoactive intestinal peptides. Epithelial membrane antigen is also often positive. MCC are usually not decorated with thyroid transcription factor–1 (TTF-1), which is an important finding because most small cell carcinomas of the lung are TTF-1 positive.