Occasional Staining for P63 in Malignant Epithelioid Vascular Tumors.
Michael E Kallen, Flavia G Nunes, Adriana L Gonzalez, Justin M Cates, Melinda E Sanders. Vanderbilt Medical School, Nashville, TN
Background: The tumor protein p63 is involved in a complicated network of molecular interactions controlling cell differentiation and proliferation, and appears to be a useful marker to differentiate between spindle cell carcinoma and sarcoma. Although preliminary studies have demonstrated excellent specificity for epithelial tumors, a limited number of sarcomas have been studied thus far. Recently, we observed serendipitous staining for p63 in an angiosarcoma of the breast. Since none of the previously reported angiosarcomas or epithelioid hemangioendotheliomas examined for p63 expression was positive, we reasoned that further investigation of p63 immunoreactivity in vascular tumors was warranted.
Design: Representative cases of conventional angiosarcoma, epithelioid angiosarcoma, epithelioid hemangioendothelioma and Kaposi sarcoma were identified retrospectively. Immunohistochemical stains for p63 were performed on one selected block from each case. Immunoreactivity was scored as either cytoplasmic or nuclear and the percentage and intensity of positive cells was recorded.
Results: Only 3 of the 35 malignant vascular tumors studied were positive for nuclear p63 (8.6%). However, all three p63-positive cases demonstrated epithelioid-type morphology, with copious eosinophilic cytoplasm. In epithelioid hemangioendothelioma, nuclear staining of moderate intensity (less intense than internal control squamous epithelia) was observed in approximately 60% of neoplastic cells in one case and between 5-10% of tumor cells in another. The one p63-positive epithelioid angiosarcoma showed strong nuclear staining in approximately 75% of cells. In two other cases each of epithelioid angiosarcoma and epithelioid hemangioendothelioma, diffuse and intense cytoplasmic staining for p63 was noted.
Conclusions: Expression of p63 in tumors of vascular differentiation is very unusual, but is seen in occasional cases with an epithelioid morphology (3 of 10 such cases). Since both epithelioid angiosarcoma and epithelioid hemangioendothelioma may also co-express cytokeratins, the finding of nuclear p63 represents another potential pitfall in the differential diagnosis between poorly-differentiated carcinomas and epithelioid vascular neoplasms.