Cutaneous Angiosarcomas - Microscopic Features : The lining endothelial cells are atypical with plump hyperchromatic nuclei. The endothelial cells may pile up within the vascular lumens creating papillations or solid nests resembling those seen in papillary endothelial hyperplasia. Mitotic activity is increased. Some angiosarcomas are well-differentiated (low-grade) and composed of innocuous-appearing anastomosing network of sinusoids lined by minimally atypical endothelium. The diagnosis in such cases is based on the infiltrative growth pattern rather than cytologic atypia.