OUTLINE: This is a randomized, double-blind, placebo-controlled, multicenter study. Patients are stratified according to treatment center and catheter placement (proximal to axilla vs distal to axilla). Patients are randomized to one of two treatment arms. Arm I: Patients receive dalteparin subcutaneously (SC) daily. Arm II: Patients receive placebo SC daily. Treatment continues for 16 weeks or until catheter removal in the absence of unacceptable toxicity. Patients are followed for 30 days.