In this xenograft model, anti-human CD34+ tumor cells were not found; anti-mouse CD31 staining showed murine tumor blood vessels at the edge of the xenograft, rarely in the center; anti-mouse CD34 staining revealed that murine tumor blood vessels outside the xenograft were surrounded by a high density of tumor cells, suggesting that SHG-139S cells invade outside along murine vascular system. This evidence concerns the gene PECAM1 and neoplasm.