Prostate cancer metastasis to bone marrow involves initial adhesion of tumor cells to the bone marrow endothelium, followed by transmigration and proliferation within the marrow. Rapid, specific adhesion of highly metastatic prostate adenocarcinoma cells Prostate cancer mortality is frequently the result of bone metastasis. The preferential homing of circulating prostate tumor cells to bone marrow is thought to involve an initial rapid adhesion to cells of the bone marrow endothelium, followed by transmigration of the endothelium, engagement of specific receptors, and subsequent proliferation within the bone marrow microenvironment. Molecular mechanisms underlying these processes are poorly understood, but there is evidence that tumor cells may exploit existing pathways utilized by circulating blood cell progenitors to gain access to bone marrow.To identify potential cell adhesion molecules involved in prostate tumor bone metastasis, research in our laboratory has focused on the interaction of prostate carcinoma cells with bone marrow endothelial cells (BMECs).1 Highly metastatic PC3M-LN4 cells (1) were found to adhere rapidly to human bone marrow-derived sinusoidal endothelial cell lines, whereas poorly metastatic LNCaP cells were only weakly adherent (2). This adhesion, specific for BMECs relative to other endothelial cells, was subsequently found to depend upon the presence of a pericellular hyaluronan (HA) matrix assembled on the PC3M-LN4 cells. The presence of pericellular HA further correlated with elevated HA synthesis and expression of HA biosynthetic enzymes in the metastatic cells. Collectively, our results may implicate tumor cell-associated HA and up-regulation of HA synthase (HAS) in prostate cancer progression, possibly by facilitating arrest in the bone microvasculature and/or preferential tissue colonization of individual tumor cells.