The deregulation of marker genes, including podoplanin (PDPN), prospero homeobox 1 (PROX-1), vascular endothelial growth factor 3 (VEGFR3) and endothelin receptor A (EDNRA), suggests that the radiation-associated breast angiosarcomas developed from radiation-stimulated lymphatic endothelial cells. Here, PROX1 is linked to breast angiosarcoma.