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


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?

The research

A summary of 21 studies published up to June 2013.

Who? The studies included almost 10,000 people of any age who had cancer at any stage and were undergoing chemotherapy. In 67% of the studies, people had advanced or metastatic cancer. They had not taken anticoagulant medications before.

What? The studies compared anticoagulant medications with placebo or inactive control.
Anticoagulant medications vs Placebo or inactive control
  • low-molecular weight heparin  (dalteparin [Fragmin], certoparin, nadroparin, or enoxaparin [Lovenox])
  • vitamin K antagonists (e.g., warfarin)
  • unfractionated heparin
  • direct thrombin inhibitors
  • factor Xa inhibitors
  In this case, a needle containing an inactive substance that has no effect on the outcome

What the researchers found

The quality of the studies ranged from low to high.

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

3 fewer people out of 100 taking low-molecular weight heparin had symptomatic venous thromboembolism.

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

The bottom line

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


Summary of findings: Low-molecular weight heparin vs inactive control in people who have cancer and are undergoing outpatient chemotherapy

Outcomes at 8 weeks to 4 years Rate of events with low-molecular weight heparin Rate of events with inactive control Absolute effect of low-molecular weight heparin Number of studies and quality of the evidence
Symptomatic venous thromboembolism 2.7% 5.8% About 3 fewer people out of 100 had a symptomatic venous thromboembolism 8 studies/moderate quality
Bleeding 2.4% 2.2% No effect* 8 studies/low quality
*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.
This Evidence Summary is based on a systematic review by 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. 25171736
If you have cancer and are receiving chemotherapy,
ask your doctor if you should get a needle to prevent blood clots in your legs.

Do I need to worry about blood clots if I have cancer and am having chemotherapy?

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.

The summary of studies by Di Nisio shows that about 6 patients out of 100 who have cancer and are on chemotherapy develop a clot; if they are given daily needles of blood thinners, 3 of them will not develop a clot. On the other hand, 97 patients out of  100 will receive needles but have no benefit and 3 of them will have a clot despite treatment.

If you have cancer, that is your most important problem. However, clots can occur, and you may be able to reduce your risk of having a clot.

Why do I need to discuss this with a doctor?

Before giving you blood thinners, your doctor has to check if you have contraindications. Also, it may or may not be good for you to take blood thinners, depending on your risk of having a clot. If you have a catheter, have had a previous clot, have a family member who has had a clot, or if you are receiving a specific type of chemotherapy, your need for a blood thinner may be stronger or weaker.

Also, blood thinners are always prescribed and monitored by a doctor—whether it be your cancer doctor, your family doctor, or a thrombosis specialist.

Published: Monday, October 31, 2016