The initial and transient interaction of tumor cells with the vessel wall can be mediated by the expression of the selectin family of adhesion molecules, including endothelial P-selectin and E-selectin, which establish and disengage low-affinity bonds that make leukocytes and tumor cells appear to “roll” on the endothelium, at least in vitro (159). The gene discussed is SELP; the disease is neoplasm.