Breast cancer is associated with a low rate of thromboembolic events (TEE) when compared to other cancers, without influence of the histological type on incidence. Risk factors include the stage of cancer, and the patients' profile and management: hospitalization, surgery and presence of a central catheter but also some cytotoxic chemotherapy, tamoxifen, and some anti-angiogenic targeted therapies. The pathophysiology of TEE includes a cross-stimulation phenomenon, involving tumor cells with procoagulant activity, and factors of hemostasis, coagulation and fibrinolysis. Circulating cellular microparticles bearing tissue factor play a major role, as well as thrombogenic platelet interactions with tumor cells via P-selectin. The occurrence of TEE in a cancer patient significantly increases the risk of death. Prevention is framed by recommendations in surgical patients. Curative treatment is based on the use of low molecular weight heparin for at least six months.