Answer: Angiosarcoma

Histology: The pancreas is involved by solid clusters of tumor cells which are essentially undifferentiated. Tumor cells have vesicular chromatin, prominent nucleoli, and show abundant mitotic activity. No overt areas of gland formation are identified. On immunohistochemical analysis, tumor cells are immunoreactive for CD34 and CD31, but not for cytokeratin AE1/AE3. There is focal labeling for cytokeratin Cam 5.2.

Discussion: Medullary Carcinoma of the pancreas is a special type of ductal carcinoma characterized by syncytial growth pattern and prominent admixed inflammation. These tumors label intensely for cytokeratins. Acinar cell carcinoma would have similar cytology, but would typically form trabecular or tubular patterns, and would label for cytokeratin. Ductal adenocarcinoma would characteristically have a desmoplastic stromal reaction and would label for cytokeratins.

This case highlights the observation that angiosarcomas of the viscera, such as the pancreas, are often epithelioid and can express cytokeratin. This creates confusion with the more common carcinomas of visceral organs.