VEGF, VEGFR1, and VEGFR2 expression in melanoma

Abstract

8520 Background: Metastatic melanoma is a chemoresistant disease with poor prognosis. Angiogenesis plays a role in progression and metastasis of melanoma. Identifying angiogenic molecules that are differentially expressed between benign and malignant tissues may enable us to create an assay to predict sensitivity to antiangiogenic agents, thus guiding selection of patients for treatment. VEGF signals through its receptor VEGFR1/flt-1 (R1) but is thought to mediate most of its angiogenic and proliferative effects through VEGFR2/flk-1/kdr (R2). In smaller melanoma studies, VEGF, R2 and less commonly R1 expression was associated with disease aggression. We characterized VEGF, R1, and R2 expression on a cohort of 540 nevi and 548 melanomas. Methods: We stained tissue microarrays to assess VEGF, R1, and R2 expression by automated quantitative analysis (AQUA), an objective method for analysis of protein levels. We used S100 to define pixels as melanoma (tumor mask) within the array spot, and measured intensity of VEGF, R1, and R2 expression using Cy5 conjugated antibodies within the mask. Results: VEGF, R1, and R2 expression was significantly higher in melanomas than in nevi by unpaired t-tests (p<0.0001). VEGF and R2 expression was higher in metastatic than primary specimens (p<0.0001). Differential expression of R1 between metastatic and primary specimens was less pronounced (p=0.0158). R2 expression correlated with Breslow depth > 2 mm (p=0.0129). Cox univariate analysis revealed an association between decreased survival and expression of VEGF (p= 0.0488) and R2 (p=0.0035); however, this was not independent of disease stage. Conclusions: VEGF, R1, and R2 expression is higher in malignant melanocytes than in their benign counterparts and higher in metastatic than primary specimens. This association with disease aggression underscores the importance of these proteins as therapeutic targets. Differential expression of R2 was found to be more significant than R1, supporting the belief that VEGF mediates its effects through R2 in malignancy. To our knowledge, this is the largest study to examine the VEGF pathway in melanoma. Future clinical trials of antiangiogenic agents in melanoma should include correlative serum and tissue assays of VEGF, R1, and R2 as biomarkers of response to therapy. [Table: see text]