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Soluble cytokines may enable tumour cells to stimulate the formation of blood vessels within melanomas of the uvea. Vascular endothelial growth factor-A (VEGF-A) and basic fibroblast growth factor (bFGF)—promotors of blood vessel development—have been shown histochemically in uveal melanomas.
VEGF-A occurred in low amounts in 22% (11/49) of melanomas, around small blood vessels deep in the tumour. bFGF was detected in 89% (42/47), located diffusely in the cytoplasm. Twenty tumours tested by reverse transcriptase PCR detected mRNA for each cytokine. The presence of VEGF-A and bFGF was not related to microvessel density or tumour cell type, location, or mitotic index. Primary cell cultures of three melanomas stimulated the growth of two established endothelial cell lines—one derived from rat brain and the other from human umbilical cord—in a dual culture system allowing diffusion of soluble substances but no mingling of the cells, suggesting “cross talk” between melanoma and endothelial cell lines . Stimulation was partially reduced with antibodies against bFGF or VEGF-A, or both, so other soluble cytokines might be involved.
Fifty uveal melanomas were excised from removed eyes. The cytokines were located immunohistochemically in formalin fixed, paraffin thin sections using several staining methods for VEGF-A, including a double antigen retrieval method to increase the chance of detection. The remaining unfixed tumour provided material for mRNA determination and tissue culture. The effects on growth of adding anti-bFGF or anti-VEGF-A antibody, or both, to the dual cell cultures was determined by ATP assay.