HMGB1 and cancer: With the aim of understanding the relevance of the CXCL12/HMGB1 heterocomplex in promoting tumor cell migration and invasion, we selected two breast (MDA-MB-231 and MCF-7) and one prostate (PC-3) cancer cell lines, characterized by different metastatic properties, for which the relevance of the CXCR4/CXCL12 axis in metastatic spread was previously established (30, 31).