The risk of thrombosis is particularly high in cancer patients, due to many associated risk factors : surgery, immobilization, central venous access, elderly patients... Furthermore, cancer induces a state of hypercoagulability. Thrombophlebitis in this context carries a poor prognosis partially explained by the link with metastasis. Various treatments further increase the risk of thrombosis. Surgery is the most studied therapeutic modality increasing the incidence. Several medical treatments might synergize increasing the thrombosis rate up to 40% for some combinations. Anti-angiogenic treatments like VEGF inhibitors, thalidomide increase the risk of thrombosis. The curative treatment of thromboses has recently been improved; a treatment by LWMH only for 3 to 6 months gives the best results. LWMH for 4 weeks has been proposed as a preventive measure after surgery only; no preventive treatment can be proposed outside this situation.