Michael L. Linenberger, MD

Thromboembolism affects many patients with solid tumors and clonalhematologic malignancies. Thromboprophylaxis with low-molecularweightheparin (LMWH) is indicated for surgery and other high-risksituations, but not routinely for central venous catheters or nonsurgical,ambulatory management. Thrombotic events require full anticoagulationfor the duration of active disease and/or the prothromboticstimulus. LMWHs are safe and more effective than both unfractionatedheparin for initial therapy and warfarin for secondary prevention. Antiinflammatoryand antiangiogenic properties might account for thisadvantage and for a survival benefit of chronic LMWH in subgroupsof cancer patients. Ongoing studies are characterizing the cost-effectivenessand antitumor mechanisms of LMWHs, the potential utility ofnewer anticoagulants, and the ability of predictive models to identifyhigh-risk candidates for thromboprophylaxis.

Thromboembolism affects many patients with solid tumors and clonalhematologic malignancies. Pathogenetic mechanisms include inflammatory-and tissue factor-mediated coagulation, natural anticoagulantdeficiencies, fibrinolytic alterations, hyperviscosity, and activationof platelets, endothelial cells, and leukocytes. High rates of venousthromboembolism (VTE) occur with advanced pancreatic, breast, ovarian,germ cell, lung, prostate, and central nervous system cancers.Hodgkin disease, non-Hodgkin's lymphoma, myeloma, paroxysmalnocturnal hemoglobinuria, and certain leukemias also predispose tovenous thromboembolism. Arterial and venous events occur with polycythemiavera and essential thrombocythemia. Central venous cathetersand prothrombotic antitumor regimens augment the risk in somepatients. Part 1 of this two-part article addresses pathophysiology, clinicalpresentations, and risk of malignancy-associated thrombosis. Part 2,which will appear in next month's issue, covers prophylaxis and treatmentof these thromboembolic complications.