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Background: Venous thromboembolism (VTE) often complicates the clinical course of cancer disease. The risk is further increased by chemotherapy but the safety and efficacy of primary thromboprophylaxis in cancer patients treated with chemotherapy is uncertain., Objectives: To assess the efficacy and safety of primary thromboprophylaxis in ambulatory cancer patients receiving chemotherapy., Search Methods: The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (last searched 3 May 2011) and CENTRAL (2011, Issue 2). The authors searched clinical trials registries and reference lists of relevant studies., Selection Criteria: Randomised controlled trials (RCTs) comparing unfractionated heparin (UFH), low molecular weight heparin (LMWH), vitamin K antagonists (VKA), direct thrombin inhibitors, direct factor Xa inhibitors or mechanical intervention to no intervention or placebo; or comparing two different anticoagulants., Data Collection and Analysis: Data were extracted on methodological quality, patients, interventions and outcomes including symptomatic VTE and major bleeding as the primary effectiveness and safety outcomes, respectively., Main Results: Nine RCTs with a total of 3538 patients were considered. None of the RCTs tested UFH, fondaparinux, direct factor Xa inhibitors or mechanical interventions. Overall, the risk of bias was low in most of the studies. LMWH, when compared with inactive control, significantly reduced the incidence of symptomatic VTE (risk ratio (RR) 0.62, 95% confidence interval (CI) 0.41 to 0.93) with no evidence of heterogeneity (I(2) = 0%). The number needed to treat to prevent a symptomatic VTE was 60. LMWH was associated with a 60% increase in major bleeding when compared with inactive control, although this was not statistically significant (RR 1.57, 95% CI 0.69 to 3.60; I(2) = 10%). There was a 45% reduction in overall VTE (RR 0.55, 95% CI 0.34 to 0.88; I(2) = 0%) while for symptomatic pulmonary embolism, asymptomatic VTE, minor bleeding and one-year mortality the differences between the LMWH and control groups were not statistically significant. The effect of the vitamin K antagonist warfarin on preventing symptomatic VTE, measured in only one study, was not statistically significant (RR 0.15, 95% CI 0.02 to 1.20). In one RCT of patients with myeloma, LMWH was associated with a 67% reduction in symptomatic VTE (RR 0.33, 95% CI 0.14 to 0.83) compared with warfarin, with no differences in major bleeding. Antithrombin, evaluated in one study on paediatric patients, had no significant effect on VTE nor major bleeding when compared with inactive control., Authors' Conclusions: Primary thromboprophylaxis with LMWH significantly reduced the incidence of symptomatic VTE in ambulatory cancer patients treated with chemotherapy. However, the lack of power hampers definite conclusions on the effects on major safety outcomes, which mandates additional studies to determine the risk to benefit ratio of LMWH in this setting.

While the association between cancer and symptomatic venous thromboembolism (VTE) is well established, the incidence and risk factors for incidental VTE in cancer patients remain unclear. The medical records of 1,921 consecutive cancer patients starting chemotherapy from January 2003 up to March 2009 were identified. Patients with a positive history of VTE were excluded. Pre-existing signs of VTE, kind and stage of malignancy, first and subsequent lines of chemotherapy, and all follow-up computed tomography (CT) scans were analysed. The primary outcome was incidental VTE. Overall, there were 101 (5.3%) VTE, 62 (3.2%) incidental and 39 (2.0%) symptomatic during a median of eight months (range 3-72). The incidence on CT scans was 0.58% (95%CI: 0.44-0.74). Incidental VTE included 24 pulmonary embolism, 28 deep venous thrombosis of the extremities, and 10 thromboses of the cava or splanchnic veins. Half of the incidental VTE occurred in the first 3-6 months of chemotherapy with a relatively higher incidence in gynecological and lung cancers. The presence of metastases, high leukocyte count, and platin-based chemotherapy increased the risk up to three-fold. All patients with incidental VTE regardless the location received half to full therapeutic doses of low-molecular-weight heparin for a minimum of three months. In summary, incidental VTE is a relative common finding in patients with solid tumours, especially in the first months of chemotherapy. Further research is needed to understand the natural history of incidental thrombosis in order to develop adequate management guidelines.