The finding of epigenetic inactivation in various human cancers of ROBO1, SEMA3B, SLIT2 and now SLIT3 and to a lesser extent SLIT1, all of which are involved in axon and cell migration in Drosophila and vertebrates, suggests a novel, and common underlying theme for these molecules in tumour suppression. The gene discussed is SLIT2; the disease is cancer.