An in vitro study performed by Mertsch et al (25) identified, using a modified Boyden chamber assay, that the Slit2/Robo1 system serves as a chemorepellent for glioma cells, indicating that glioblastoma cells migrate away from increased Slit2 concentrations and prompt Robo1-positive glioma cell invasion along gray matter tracts and into white matter, including the corpus callosum (25). This evidence concerns the gene SLIT2 and glioma.