Venous thrombosis development is the most important causes of morbidity and mortality in the cases with carcinoma. Besides prevention and treatment of the disease, studies clarifying pathophysiology are required in clinical studies. It is possible to research the initiating factors of forming thrombus in two groups; intravenous and extravenous. Intravenous factors: tissue factors, carcinoma procoagulant, TNF secreted from carcerous cells, IL1, plasminogen activator inhibitor, mucin, thrombomodulus, ADP, heparin sulphat, annexing II can be considered. Extravenous factors are the size of cancerous mass, histopathologic diagnoses, the pressure it causes, vascular wall damage, venous stasis, lengthened immobilization, chemotherapy and surgical interventions. By supporting these factors that contribute to forming thrombosis in the cancer patients with the literature data, treatment choices against the risk of thrombosis will be suggested with the help of guides. © IDOSI Publications, 2012.