AbstractThe progressive growth of solid tumors is dependent on the tumor ability to recruit new blood vessels from the surrounding host tissues. We show here that acidic Fibroblast Growth Factor (FGF-1) produced by a rat bladder carcinoma transfected cell line (NBT-II cells) is a potent inducer of angiogenesis. After injection in nude mice, NBT-II cells transfected with FGF-1 form rapidly growing carcinomas which are highly vascularized, whereas carcinoma cells producing a biologically active form of FGF-4 behave like non-producer cells. The vasculature of the tumors obtained with NBT-II cells producing a secreted form of FGF-1 is dramatically expanded but lacking in some places a complete endothelial lining. Conditioned medium from these cells induce formation of capillary-like structuresin vitro, whereas those of FGF-4 and non-secreting FGF-1 producing cells failed to induce such structures.Our results indicate that the expression of FGF-1 may promote tumor growth, at least in part, by inducing angiogenesis, and that the acquired ability of tumor cells to secrete FGF-1 but not FGF-4, may result in aberrant neovascularization of the tumor.