A Cochrane review included 4 studies with a total of 1242 subjects. The included studies evaluated prolonged thromboprophylaxis with LMWH as compared to control or placebo in major abdominal or pelvic surgery. 2 studies included only high risk cancer patients undergoing surgery for abdominal or pelvic cancer whereas 2 studies included patients undergoing major abdominal surgery for either malignant or benign diseases. It was not possible to make a comparison between cancer and non-cancer patients, because no separate data was provided from patients with and without cancer. The incidence of overall venous thromboembolism (VTE) was 14.3% in the control group and 6.1% in the patients receiving out-of-hospital LMWH (Peto OR 0.41, 95% CI 0.26 to 0.63; NNT 13). Prolonged thromboprophylaxis with LMWH was also associated with a statistically significant reduction of even the incidence of symptomatic VTE from 1.7% in the control group to 0.2 % in patients receiving prolonged thromboprophylaxis (Peto OR 0.22, 95% CI 0.06 to 0.80; NNT 66). The respective incidence of bleeding in the control and LMWH group were 3.7% and 4.1% (Peto OR 1.11, 95% CI 0.62 to 1.97). The studies included in the present meta-analysis were not designed to detect a reduction of PE or mortality; there was no significant difference in the mortality rate between the two allocation groups.