PECAM1 and angiosarcoma: CD31 is the most sensitive vascular marker for angiosarcoma diagnosis.[6] More than 90% of CD31 expression is observed in angiosarcoma, but <1% of CD31 is positive for cancer cells.[1] Therefore, CD31 is considered to provide a relatively high sensitivity and specificity index.[11] The rate of CD34 positivity is 40%–100%, which is easy to stain in the obvious angiogenic region.