FIGURE 2. Potential mechanisms of action by which ICAM-1 may promote tumor metastasis.
(1) Via binding to β2-integrins expressing tumor cells, ICAM-1 may support homotypic clustering of circulating tumor cells (CTCs). CTC clusters showed increased survival and metastatic potential. (2) Via β2-integrins expressed by immune cells, ICAM-1 can promote CTC-leukocyte clustering β2-integrin. Association of CTC clusters with polymorphonuclear neutrophils increased survival and proliferation of tumor cells. (3) ICAM-1 expressed by endothelial cells can facilitate capture and extravasation of β2-integrin-expressing tumor hijacking transendothelial migration mechanisms used by migrating leukocytes