Can any other tumors be microscopically confused with MCC?

Yes. MCC is composed of undifferentiated basaloid, small, blue cells with hyperchromatic nuclei, scant cytoplasm, and frequent mitotic figures, and it may be confused with metastatic small cell carcinoma (oat-cell carcinoma) of the lung, malignant lymphoma, sweat gland carcinoma, metastatic carcinoid tumors, and Ewing’s sarcoma. Electron microscopy may be helpful in order to highlight the dense core neurosecretory granules seen in MCC.