PPBP and cancer: TCGA database indicated that among several ligands, CXCL1, CXCL3, CXCL5, CXCL7 and CXCL8 (ligands for CXCR2) and CCL15 (ligand for CCR1) were particularly upregulated in CRC tissues compared with other cancers (Fig. 1a and Supplementary Fig. 1a).