Unusual organelles in an epithelioid angiosarcoma

We recently encountered unusual organelles in a tumor from a 75-year-old white British female presenting with a scalp lesion which histologically was a poorly differentiated malignant neoplasm (Fig. 1). On the basis of histology and immunohistochemistry [positive staining for factor Vlll-related antigen (Fig. 2), JC70A (CD31),¹ and Ulex europaeus agglutinin 1] the tumor was diagnosed as an epithelioid angiosarcoma. An unexpected finding was that some unambiguous tumor cells were positive for S100 protein. Occasional S100 protein-positive dendritic cells, interpreted as reactive Langerhans cells, were also present. To confirm a confidently held diagnosis, but one which was nevertheless uncertain because of the S100 protein staining, electron microscopy was conducted. Not unexpectedly, Weibel-Palade bodies were not identified,² but the rough endoplasmic reticulum, polyribosomes, aggregates of haphazardly arranged intermediate filaments, and a well developed lamina were seen as being consistent with epithelioid angiosarcoma.