A study looking at heparin for blood clots caused by cancer (ALICAT)

Cancer type:

All cancer types




Phase 2

This study looked at how long people should be treated with heparin for blood clots caused by cancer. It was for people who had already had heparin to treat their blood clot for about 6 months. They also had cancer that had spread into surrounding tissue, or elsewhere in the body.

More about this trial

Blood clots (thrombosis) are more common in people who have cancer. Doctors know that cancer cells can release chemicals that make the blood thicker than usual, and so more likely to form a clot.

A blood clot in an arm or leg is called a deep vein thrombosis or DVT. It can cause redness, pain and swelling. If bits of the clot break off and are carried to the lungs, they can cause a blockage called a pulmonary embolism or PE. You may have a sudden cough, chest pain or breathlessness. The clots need treatment as some may be life threatening.

If you have a blood clot, you will have a drug to stop others forming, while the body reabsorbs the clot itself. At the moment, the standard treatment Open a glossary item for treating blood clots caused by cancer is low molecular weight heparin. It is currently licensed Open a glossary item to be used for 6 months.

Some doctors prefer to use it for longer in people with cancer that has spread. This is because having cancer may continue to make the blood sticky and increase the risk further blood clots.

The study team planned to compare patients who continued heparin treatment for a further 6 months with people who stopped the heparin.

This was a feasibility study. Its aims were to

  • Find out if people were willing to take part in this study
  • Find out what people thought about the study and the reasons why they would or would not take part
  • Find out whether doctors wanted their patients to take part in the study

If the feasibility study was successful, the researchers planned to carry out a phase 3 trial. In this trial they would try to find out whether treatment with 1 year of heparin was better than 6 months for people with cancer.

Summary of results

The researchers found the planned phase 3 randomised trial was not feasible. This was because not enough people would agree to take part in this type of trial.

The researchers interviewed people who were willing to take part in a trial and those who weren’t. They also interviewed the people’s doctors.

From these interviews it seems that people did not want to take part because they had fixed views on what the length of treatment should be.


  • Some patients preferred the idea of ongoing treatment, others did not want treatment beyond 6 months. This preference was probably based on past experience
  • Patients who had symptoms when they were diagnosed with a blood clot and whose symptoms improved with heparin treatment were more likely to want to continue with treatment
  • Patients who did not have symptoms and were diagnosed with a blood clot incidentally were more likely to see heparin treatment as an inconvenience and wanted to stop treatment at 6 months
  • People with cancer did not want to be part of a randomised trial that might change their preferred course of treatment


Doctors appeared unwilling to recruit their patients on to the study because

  • The preferred choice of doctors was mainly treatment with heparin for 1 year
  • Doctors tended not to ask those patients they thought were at a higher risk of developing another blood clot because they wanted to make sure they had a longer treatment with herparin

The researchers felt the length of heparin treatment was still an important research question. But from their experience this would be difficult to look at in a trial setting.

There are other areas of research they think would be useful to look at. For example, comparing new anti-coagulants (blood thinning) drugs you take by mouth (orally) with low molecular weight heparin. And looking at the risk and treatment of blood clots for people with certain types of cancer, such as breast cancer.

We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) and published in a medical journal. The figures we quote above were provided by the trial team who did the research. We have not analysed the data ourselves.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Dr Simon Noble

Supported by

Cancer Research UK
Cardiff University
NIHR Clinical Research Network: Cancer
NIHR Health Technology Assessment (HTA) programme

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 10700

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Charlie took part in a trial to try new treatments

A picture of Charlie

“I think it’s really important that people keep signing up to these type of trials to push research forward.”

Last reviewed:

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