Evidence Summary

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Low-molecular weight heparin reduces venous thromboembolism in people with cancer who are undergoing outpatient chemotherapy

Di Nisio M, Porreca E, Otten HM, et al. Primary prophylaxis for venous thromboembolism in ambulatory cancer patients receiving chemotherapy. Cochrane Database Syst Rev. 2014;8:CD008500.

Review questions

In people who have cancer and are undergoing outpatient chemotherapy, do anticoagulant medications (“blood thinners”) prevent venous thromboembolism (blood clots in the veins)? Are they safe?


People who have cancer are more likely to develop blood clots in their veins, and this risk is higher when they are undergoing chemotherapy. These blood clots increase the risk of death. Anticoagulant medications can prevent blood clots, but they can also cause serious bleeding.

How the review was done

The researchers did a systematic review searching for published studies up to June 2013. They found 21 randomized controlled trials with 9861 people.

In the trials, people of any age had solid (tumour-based) or hematological (blood cell–based) cancer at any stage and were undergoing chemotherapy. They had not taken anticoagulant medications before.

Anticoagulant medications included low-molecular weight heparin (i.e., dalteparin [Fragmin®], certoparin, nadroparin, or enoxaparin [Lovenox®]); vitamin K antagonists (e.g., warfarin), unfractionated heparin, direct thrombin, or factor Xa inhibitors.

Anticoagulation medications were compared with a placebo or an inactive control.

Outcomes were symptomatic venous thromboembolism and major bleeding.

What the researchers found

Quality of the trials ranged from low to high.

People had advanced or metastatic cancer in 14 of the 21 trials.

There was not enough evidence to assess vitamin K antagonists, unfractionated heparin, or direct thrombin or factor Xa inhibitors.

27 fewer people out of 1000 taking low-molecular weight heparin had symptomatic venous thromboembolism.

There was no effect of low-molecular weight heparins on major bleeding, but the quality of evidence was low.


In people who have cancer and are undergoing outpatient chemotherapy, low-molecular weight heparin reduces symptomatic venous thromboembolism.

Anticoagulant medications (low-molecular weight heparin) vs inactive control in people who have cancer and are undergoing outpatient chemotherapy

Outcomes at 8 weeks to 4 years

Number of trials

Rate of events with low-molecular weight heparin

Rate of events with inactive control

Absolute effect of anticoagulant medications

Quality of the evidence

Symptomatic venous thromboembolism




27 fewer people out of 1000 had a venous thromboembolism


Major bleeding




No effect*


*Although the rates for the 2 groups look different, the differences were not statistically significant—this means that the difference could simply be due to chance rather than due to the different treatments.



A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

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