Immunohistochemical expression and distribution of VEGFR-3 in malignant mesothelioma.

Homogeneity of mesothelial and lymphatic endothelial cells, express some markers that are presumed to be exclusive of the endothelium was recently reported. This similarity is important to improve the diagnosis and prognosis of malignant mesothelioma (MM). Additionally, some of these markers provide the rationale for specific molecular-targeted novel therapies aimed at MM, an aggressive malignant neoplasm, with an usually dismal prognosis. The goal of our study was to determine the prevalence and expression pattern of VEGF receptor-3 (VEGFR-3) immunoreactivity in MM and whether this immunoreactivity occurs in different phenotypes of this neoplasm. Formalin-fixed and paraffin-embedded samples from 29 MM cases and 5 metastatic carcinomas were immuno-stained for VEGFR-3 according to the streptavidin-biotin-peroxidase complex technique using a primary antibody (Zymed Laboratories, CA, USA) diluted at 1:200. Lymphatic vessels (LV) were outlined mainly in the peripheral area surrounding the neoplasms. Blood vessels were only rarely positive for VEGFR-3 in a pattern easily distinguishable from LV. In 25 out of 29 cases (86.2%) LV were strongly positive for VEGFR-3: 14 cases (48.2%) exhibited positive VEGFR-3 reactivity in malignant cells. Epitheliod MM showed a moderate to intense VEGFR-3 positive reaction in LV from 8 out of 19 cases. Among the other histological subtypes, a positive VEGFR-3 reaction was noted in malignant cells from two cases of transitional and one case of pleomorphic MM. Malignant cells from two out of three biphasic and one out of three sarcomatoid MM were also positive for VEGFR-3. Interestingly, one case of the multicystic subtype was negative for VEGFR-3 in malignant cells and faintly positive in an occasional LV. All cases of metastatic carcinoma were negative for VEGFR-3 in the neoplastic cells. In conclusion, VEGFR-3 was expressed in malignant cells from different subtypes of MM, reinforcing the putative role of this marker as a potential therapeutic target in this group of neoplasia.