We have shown that given cytokines are capable of inducing the expression of transcription factors of the Ets family in two very distinct cell types: 1) endothelial cells of blood vessels, but only during neovascularization, and 2) fibrocytic cells from stroma surrounding tumors, but only if these tumors bear characteristics of invasiveness. In such cases, the fibrocytic cells also express some metalloproteinases (collagenase 1, urkinase plasminogen activator, sometimes stromelysin1). In ex vivo reconstruction experiments, we demonstrate that the corresponding genes are directly up-regulated by the Ets family transcription factors, often associated with the transcription complex Jun/Fos. The proteinases are thought to dismantle the stroma and allow invasive tumors to proceed toward further expansion. We speculate that inactivation of the Ets factors could seriously hamper both neovascularization and tumor expansion.