VAV1 and lung cancer: Taken together, the results thus far raise the possibility that Vav1 in lung cancer cells instigates a positive feed forward loop, which is amplified in the presence of macrophages: Vav1 stimulation induces cytokine secretion, which in turn activate macrophages to upregulate Vav1 expression (and possibly other cytokines such as EGF as well), resulting in increased ERK activation.