Occasional staining for p63 in malignant vascular tumors: a potential diagnostic pitfall.

Expression of p63, a putative marker for epithelial or myoepithelial differentiation, has been used to distinguish spindle cell carcinoma from sarcoma. The specificity of p63 for epithelial differentiation has not been thoroughly evaluated however, since p63 expression has been explored in only a handful of mesenchymal tumors. After observing unexpected immunohistochemical staining for p63 in an angiosarcoma of the breast, we evaluated a series of benign and malignant vascular tumors to determine the frequency of such a finding. Nuclear immunoreactivity to p63 was detected, at least focally, in 24% of malignant vascular tumors other than Kaposi sarcoma, which was uniformly negative. Benign vascular tumors were also negative for p63. Although p63 expression in tumors of vascular differentiation is unusual, it may be seen occasionally in some malignant vascular tumors. Thus, p63 is not entirely specific for epithelial differentiation. Since soft tissue angiosarcomas and hemangioendotheliomas sometimes express cytokeratins, the finding of nuclear p63 represents another potential pitfall in the differential diagnosis between poorly-differentiated carcinomas and vascular neoplasms.