Splenic hemangiosarcoma with sinus endothelial differentiation.

A case of primary splenic hemangiosarcoma where the tumors entirely replaced the spleen is reported. Histologically, the splenic tumors consisted of two major components: (i) solid and nodular areas, in which spindle cells (SC) were arranged in interlacing fascicles; and (ii) vasoformative areas, in which vascular lining cells (VC) closely resembled normal splenic sinus endothelial cells (SSEC) in shape. Both SC and VC were immunoreactive with the markers of vascular endothelial cells (EC) including SSEC, JC70, von Willebrand factor, OKM5, vimentin MAb and Ulex europaeus-1 lectin. The tumor cells were positive for OKM5 MAb as well as normal SSEC and sheathed arterial EC, but other vascular EC in normal spleen were negative. Enzyme-histochemically, the tumor cells and normal SSEC revealed naphthol AS-D acetate esterase activity but no reaction for ALPase, whereas normal vascular EC other than SSEC in the spleen were positive for the latter but negative for the former. These studies revealed that the tumor cells expressed the same phenotype as normal SSEC. To the present author's knowledge this is the first report demonstrating sinus endothelial differentiation of splenic hemangiosarcoma, enzyme- and immuno-histochemically.