Our data suggest that migration of ccRCC cells follows the latter mechanism as inhibition of Rac1 abolished the spindle-like mesenchymal cell morphology of Activin B expressing cells and inhibited their invasion, whereas activation of Rac1 sufficed for re-establishing mesenchymal morphology and invasiveness in Activin B knockdown cells. The gene discussed is RAC1; the disease is nonpapillary renal cell carcinoma.