SLIT2 and neoplasm: However, asporin expression appears to be influenced by the tumour’s genetic subtype, suggesting that the level of fibroblast-induced tumour suppression can be partly determined by the tumour itself.65 Likewise, breast tumours can downregulate the roundabout homologue 1 (Robo1) receptor to stop the tumour-suppressive effects of its fibroblast-derived ligand, slit homologue 2 (SLIT2), which inhibits proliferative β-catenin signalling.