That's not exactly news. Doctors have known for 137 years that cancer patients risk blood clots in veins deep in the legs that can dislodge and block blood flow in the lungs. But now a Dutch research team shows that the risk is considerably higher than previously thought, and their study offers data that may help patients avoid this deadly complication.
In the first three months after cancer diagnosis, the risk of blood clots is 53 times higher than for people without cancer. Patients whose cancer has spread to other parts of the body have a 20 times higher risk than cancer patients without distant spread.
At highest risk are patients with blood cancers, who have a 28 times higher risk than people without cancer. Also at high risk are patients with lung cancer and with gastrointestinal cancers.
Gene mutations that predispose a person to blood clots also increase cancer patients' risk, although the mutations are rare enough to argue against screening. Jeanet W. Blom, MD, and colleagues report the findings in the Feb. 9 issue of The Journal of the American Medical Association.
"It may be more cost-effective to consider [preventive] anticoagulant therapy for patients with cancer who have an increased risk to develop [blood clots]," Blom and colleagues write. "However, since these patients also have an increased risk of hemorrhage, this needs to be cautiously evaluated."
Two years after cancer diagnosis, the risk goes way down. But it doesn't entirely go away until 15 years after the cancer is found.
It's not entirely clear how much of the risk is due to the cancer itself and how much is due to cancer treatment. There are a lot of ways cancer can lead to clotting problems. But cancer therapies themselves increase blood clotting.
There are warning signs of blood clots. When a blood clot forms in the leg, patients complain of persistent or worsening cramps in the calf or a charley horse. The lower part of the leg may swell and discolor. Sometimes cancer patients will have blood clots in the arms. In this case there may be swelling in the arm or neck.
When a blood clot breaks off from a vein it can become lodged in the lungs, causing a pulmonary embolism. Symptoms of pulmonary embolism include:
- Unexplained shortness of breath
- A sense of general anxiety
- Chest discomfort that is usually worse with a deep breath or cough
- Light-headedness or fainting spells
If you have these symptoms, especially if you have cancer or another risk factor for blood clots, such as heart failure, use of oral contraception, or pregnancy, you should seek immediate medical attention.