Blood thinners for the prevention of clots in patients with cancer undergoing surgery


Patients with cancer undergoing surgical procedures are at an increased risk of blood clots. The blood thinner administered to prevent these clots can be either an unfractionated heparin (UFH) or low molecular weight heparin (LMWH). These two blood thinners may have different effectiveness and safety profiles.

Study characteristics

We searched scientific databases for clinical trials looking at the effects of UFH and LMWH on death, pulmonary embolism (blood clot in the lungs), deep vein thrombosis (blood clot in the veins of the legs), bruising, bleeding, and need for blood transfusion in patients having operations. We included people of any age or sex. The evidence is current to February 2013.

Key results

We found 16 studies of 12,890 patients with cancer. There was no evidence to show that LMWH was better than UFH for death, asymptomatic deep vein thrombosis, pulmonary embolism, or bleeding. There was less bruising around the wound and more blood transfusion during the operation with LMWH compared with UFH. Further trials are needed to clarify the effectiveness of LMWH and UFH.

Quality of evidence

The overall quality of evidence of these studies was moderate.

Authors' conclusions: 

We found no difference between perioperative thromboprophylaxis with LMWH versus UFH in their effects on mortality, thromboembolic outcomes, major bleeding, or minor bleeding in patients with cancer. Further trials are needed to evaluate the benefits and harms of different heparin thromboprophylaxis strategies in this population more thoroughly.

Read the full abstract...

The choice of the appropriate perioperative thromboprophylaxis in patients with cancer depends on the relative benefits and harms of low molecular weight heparin (LMWH) and unfractionated heparin (UFH).


To update a systematic review of the evidence for the relative efficacy and safety of LMWH and UFH for perioperative thromboprophylaxis in patients with cancer.

Search strategy: 

We performed a comprehensive search for trials of anticoagulation in patients with cancer including a February 2013 electronic search of: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE. We also handsearched conference proceedings, reviewed reference list of included studies, used the 'related citations' feature in PubMed, and searched for ongoing studies.

Selection criteria: 

Randomized controlled trials (RCTs) that enrolled patients with cancer undergoing a surgical intervention and compared the effects of LMWH to UFH on mortality, deep venous thrombosis (DVT), pulmonary embolism (PE), bleeding outcomes, or thrombocytopenia.

Data collection and analysis: 

Two review authors independently used a standardized form to extract in duplicate data on participants, interventions, outcomes of interest, and risk of bias. Where possible, we conducted meta-analyses using the random-effects model.

Main results: 

Of 9559 identified unique citations, we included 16 RCTs with 12,890 patients with cancer, all using preoperative prophylactic anticoagulation. We identified no new study with this update. The overall quality of evidence was moderate. The meta-analyses did not conclusively rule out either a beneficial or harmful effect of LMWH compared with UFH for the following outcomes: mortality (risk ratio (RR) 0.89; 95% confidence interval (CI) 0.74 to 1.08), PE (RR 0.73; 95% CI 0.34 to 1.54), symptomatic DVT (RR 0.50; 95% CI 0.20 to 1.28), asymptomatic DVT (RR 0.81; 95% CI 0.66 to 1.01),major bleeding (RR 0.85; 95% CI 0.52 to 1.37), and minor bleeding (RR 0.92; 95% CI 0.47 to 1.79). LMWH was associated with lower incidence of wound hematoma (RR 0.68; 95% CI 0.52 to 0.88) but higher volume of intraoperative transfusion (mean difference (MD) 74 mL; 95% CI 47 to 102). The meta-analyses found no statistically significant differences for any of the following outcomes: reoperation for bleeding (RR 0.72; 95% CI 0.06 to 8.48) , intraoperative blood loss (MD= -6mL; 95% CI -85 to 72), postoperative transfusion (MD= 79mL; 95% CI -54 to 211), postoperative drain volume (MD= 27mL; 95% CI -44 to 98), and thrombocytopenia (RR 1.33; 95% CI 0.59 to 3.00).