TUESDAY, Feb. 8, 2005 (HealthDay News) -- Cancer patients face a sevenfold increased risk for blood clots in their legs or lungs than people of similar age without cancer, a new study finds.
The risk can vary greatly depending on the type of cancer, the amount of time since the cancer diagnosis was made, whether the cancer has spread and whether the person has a hereditary mutation that affects blood clotting.
Giving anti-clotting drugs to high-risk individuals, rather than screening for potential mutations, would be an effective strategy to deal with this problem, the study authors concluded.
Their findings appear in the Feb. 9 issue of the Journal of the American Medical Association.
Experts had known that cancer patients were at a higher risk for blood clots, but it had not been clear who was at the highest risk and what factors affected that risk. Clots can partially or completely block the flow of blood in a vessel, leading to the potential for stroke and even death.
"Cancer notoriously has been found to be associated with blood clots," said Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Clinic Foundation in New Orleans.
Overall, about 4 percent to 20 percent of people with deep vein thrombosis (leg clots) or pulmonary embolism (a clot in the lung) have cancer, the study authors said.
In addition, healthy people with the factor V Leiden mutation or the prothrombin 20210A mutation have an increased risk of clots.
"In the [general] population, 6 to 10 percent of individuals have one of these two mutations," said senior study author Dr. Frits Rosendaal, a professor of clinical epidemiology at Leiden University Medical Center in the Netherlands.
To better ascertain the risk of blood clots in cancer patients, the Dutch researchers looked at 3,220 people aged 18 to 70 with a clot in the leg or lung who were being treated at one of six different anti-coagulation clinics in the Netherlands. They were compared to 2,131 healthy control patients.
Overall, people with cancer had about seven times the risk of developing a blood clot, compared to those without cancer.
People with blood-related cancers had the highest risk (28 times) of a clot, followed by lung cancer and gastrointestinal cancer, which both had 20 or more times the risk, the study reported.
The risk of a clot was highest during the first three months after diagnosis (53 times greater risk), compared to people without cancer. After two years, the risk had gone done but was still elevated compared with healthy people. Only after 15 years did the risk return to normal levels, the study said.
Patients whose cancer had spread had 60 times the risk of a clot compared with healthy people, and 20 times the risk compared with people whose cancer had not spread.
Cancer patients who were also carriers of the factor V Leiden mutation had a 12-fold increased risk of a clot, compared to individuals without cancer who did not have the mutation. Patients with the prothrombin 20210A mutation had 17 times the risk.
Screening for the mutations would not be a useful tool because it would prevent only seven to 27 clots per 10,000 cancer patients a year, Rosendaal said.
It would make more sense to give prophylactic anti-clotting drug therapy to patients with cancer who had an elevated risk of clots, such as those with a blood cancer, lung or gastrointestinal cancer, those newly diagnosed and those with tumors that have spread to other parts of the body, he said.
Therapies include oral drugs such as warfarin or injections such as heparin, Rosendaal said.
Brooks said that, thanks to the new study, "I now have markers that I can look at to see if patients are at high risk. I may want to place these people on agents to try to prevent them from developing clots."
For more on blood clots, visit the National Library of Medicine.