The ability of malignant neoplasms to metastasize is probably the most important obstacle to the survival of the cancer patient. A rate-limiting step in the metastatic cascade is the arrest and adhesion of tumor cells to the endothelium or subendothelial matrix comprising the vessel wall. This process of tumor cell interaction with the vessel wall has been previously analyzed at the molecular level with the "docking and locking" hypothesis . The hypothesis divides tumor cell interaction with target organ endothelium into 2 interdependent yet distinct steps. Initial interaction between rolling tumor cells and the underlying endothelium is mediated by relatively weak and transient adhesions. The second-phase, tighter adhesion, i.e., "locking", relies on adhesion receptors present on both tumor cells and the endothelium and is regulated by various bioactive mediators elaborated by tumor cells, endothelial cells and possibly other host cells such as platelets . Experiments indicate that this second phase is primarily mediated by integrin receptors present on the tumor cells (e.g., aIIbp3; Grossi et a/., 1989) as well as endothelium (e.g., 0593; Tang et a/., 1993a, 1994). Among the many modulators which can influence tumor cell interaction with endothelium are bioactive lipids such as the eicosanoids .Metabolites of arachidonic and linoleic acid have been demonstrated to bidirectionally modulate tumor cell interaction with the endothelium and SEM (Grossi et a!., Liu et al., 1991). Honn et al. (1989) have demonstrated that a lipoxygenase metabolite of arachidonic acid, i.e., 12(S)-HETE, increases tumor cell adhesion to SEM and components of subendothelial matrix. This effect is antagonized by a 15-lipoxygenase metabolite of linoleic acid, i.e., 13(S)-HODE (Grossi et al., 1989; Liu et al., 1991). In fact, bidirectional modulation of integrin receptor expression and tumor cell adhesion by 12(S)-HETE and 13(S)-HODE has been observed at the level of PKC (Liu et al., 1994). In addition to these lipoxygenase metabolites, cyclooxygenase metabolites of arachidonic acid, i.e., PGIz and TXA2, have been shown to modulate tumor cell-vessel interactions as well as metastasis . PG12 is a potent inhibitor of platelet activation and aggregation and is the predominant cyclooxygenase metabolite produced by endothelium. have shown that exogenous PGIl inhibits lung colony formation by murine B16a cells injected i.v. into syngeneic animals. This experimental finding established that PG12 possesses antimetastatic activity and that it may have clinical significance in oncology. In addition, Honn et a/. (1983) proposed that endogenous production of PGIz by endothelium may constitute a natural deterrent to hematogenous metastasis. Since those initial studies the anti-metastatic effects of PGI2 and PG12 analogs have been observed in a wide spectrum of tumor cells from different species and of different histopathological types (reviewed in Honn et al., 1992). It has been previously shown by our laboratory that 12(S)-HETE and TPA increase surfa...