SLIT2 and neoplasm: Consistent with these findings, conditioned media from COS cells overexpressing the tumour suppressor gene SLIT2, one of the most positively polarized genes (pol = 0.99) which is expressed at higher levels in normal prostate tissue compared to tumour (S5A Fig), was able to dramatically reduce tumour cell clone formation in a Matrigel in vitro Clonogenic assay (Fig 5G).