Tumour cell extravasation is a key event for metastatic colonisation1. However, little is known about the signalling pathways that govern tumour cell adhesion to the endothelium and subsequent transmigration through the blood vessel wall. Here, we combine Stable Isotope Labelling by Amino acids in Cell culture (SILAC) and global phosphoproteomic analysis to identify cell-specific signalling pathways regulated between interacting tumour and endothelial cells. We identified over 2,000 unique phosphorylation sites, where 77 were specifically regulated in the tumour cells and 43 in the endothelial cells.