Differential Prox-1 and CD 31 expression in mucousae, cutaneous and soft tissue vascular lesions and tumors.

The study of lymphatic vessels and lymphatic tumors has been hampered with difficulty due to the overlapping morphological features between blood and lymphatic endothelial cells, as well as to the lack of specific lymphatic endothelial markers. Over the last few years, lymphatic vessels and lymphangiogenesis have received great attention owing to their putative implications in terms of metastatic dissemination and the promise of targets for lymphangiogenic therapy. Prox-1 is a nuclear transcription factor that plays a major role during embryonic lymphangiogenesis and is deemed to be a useful marker for differentiating lymphatic endothelial cells from the other blood vessels endothelial cells. Here, we describe a double-immunostaining strategy for formalin-fixed, paraffin-embedded tissues that aims at evaluating the distribution of Prox-1 and CD 31 - a cytoplasmic pan-endothelial marker - in a series of 28 mucousae, cutaneous and soft tissue vascular lesions and tumors, including hemangiomas, lymphangiomas, lymphangiectasia, and Kaposi's sarcomas. Our results showed that in non-lesional mucousae and skin, Prox-1 decorated exclusively the nuclei of endothelial cells in lymphatic vessels. Prox-1 stained almost all the benign lymphatic vascular lesions/tumors (91%) and was absent or only focally positive in 75% of blood vascular tumors. CD 31 stained endothelial cells of blood vessels of superficial and deep dermal plexuses, lymphatics, and all blood vascular lesions/tumors. Kaposi's sarcomas were all positive for both CD 31 and Prox-1 markers. In conclusion, although Prox-1 expression in vascular lesions/tumors was not entirely restricted to tumors with known lymphatic differentiation, CD 31/Prox-1 double-immunolabeling can be used as an adjunct marker to identify lymphatic vessels in routinely processed formalin-fixed, paraffin-embedded samples.