CALCA and Merkel cell skin cancer: They express epithelial markers such as AE1/AE3, CAM 5.2, pancytokeratin, epithelial membrane antigen, and Ber-EP4 and possibly stain different neuroendocrine markers, including chromogranin, synaptophysin, calcitonin, vasoactive intestinal peptide, and somatostatin receptor.16 MCC can be differentiated by being stained with low-molecular-weight cytokeratins (eg, CK20, CK5/6) from other undifferentiated tumors (Table 1).