Endothelial cell-specific markers and Ki-67 immunolabeled in original HSAs and xenograft HSA tumors. Immunolabeling of CD31, vWF, and Ki-67, in original HSAs and xenograft HSA tumors. All original HSAs had membrane immunoreactivity for CD31 (A: the original tumor of Sa) and cytoplasmic immunoreactivity for vWF (C: the original tumor of Sa). Immunoreactivity for CD31 (B: Sa) and vWF (D: Sa) in all xenograft HSA tumors was detected in the same location as in the original tumors. In all xenograft HSA tumors, Ki-67 (E: Sy) nuclear immunoreactivity was observed in the nuclei of the tumor cells that were derived from canine HSA. Immunohistochemistry (IHC); bars: 50 μm.