OUTLINE: This is a randomized study. Patients are stratified according to prognostic index (good vs bad vs unsure), current therapy (systemic vs radiation vs both vs none), age (50 or under vs over 50), disease site (breast vs colon vs small cell lung vs nonsmall cell lung vs prostate), history of prior thrombotic event over 1 year ago (yes vs no), and gender. Patients are randomized to receive low molecular weight heparin (dalteparin) plus standard therapy or standard therapy alone.