QBEND/10, a new monoclonal antibody to endothelium: assessment of its diagnostic utility in paraffin sections.

The immunoreactivity of a new monoclonal antibody to endothelium. QBEND/10, in formalin-fixed, paraffin-embedded sections from a variety of vascular and lymphatic tumours is described and compared to that of two other endothelial markers, von Willebrand factor and Ulex europaeus agglutinin, type 1. All the benign tumours of blood vascular origin showed immunoreactivity whereas only five out of eight lymphangiomas demonstrated a weak focal reaction with QBEND/10. Primitive lumina in epithelioid and spindle cell haemangioendotheliomas were highlighted in all the cases. Tumour cells in angiosarcoma forming vasoformative areas and solid areas showed immunopositivity to QBEND/10 in 17/23 and 13/24 cases respectively, and complementary immunoreactivity for von Willebrand factor was observed. Proliferating vessels and the majority of spindle cells in Kaposi's sarcoma were positive in all 40 cases. Only one of 54 cases of carcinoma showed luminal reaction to QBEND/10. However, 17 of 45 spindle cell tumours displayed a positive reaction. QBEND/10 is an additional marker for demonstrating endothelial differentiation and has some advantages over currently available antibodies.