According to a recent Swedish study, a family history of blood clots has a greater impact on the risk of developing blood clots in multiple myeloma patients than in the general population.

“There are probably synergistic effects; i.e., if you have a family history [of blood clots] and multiple myeloma, the risk is more then the sum of the individual risks,” explained Dr. Sigurdur Kristinsson of the Karolinska University Hospital in Sweden and lead investigator of the study.

Based on the study’s findings, Dr. Kristinsson said, “Perhaps family history should be taken into account when choosing thrombosis prophylaxis [preventative care for blood clots] in myeloma patients treated with medications known to increase the risk of thrombosis, like thalidomide and Revlimid.”

However, the investigators suggest that the impact of a family history of blood clots should be further investigated.  They explained that, due to the study’s retrospective nature, family history and clinical data regarding other potential risk factors for blood clots were incomplete.

Prior studies have shown that multiple myeloma patients are at risk of developing blood clots in the veins, a condition called venous thromboembolism. If a clot breaks off and travels through the vein, it can block blood flow to vital organs, such as the lungs or the brain.

Patients receiving Revlimid (lenalidomide) or thalidomide (Thalomid) in combination with dexamethasone (Decadron) are at an even higher risk of developing blood clots (see related Beacon news).

The International Myeloma Working Group recommends that myeloma patients who are at high risk of developing blood clots take an anticoagulant, such as warfarin (Coumadin) or heparin, while being treated for myeloma.  The group recommends that standard-risk patients take aspirin (see related Beacon news).

However, before administering such preventative treatment, physicians must first identify patients who are at high risk for blood clots. Currently, a family history of blood clots is not considered a risk factor in determining preventive measures for patients receiving Revlimid or thalidomide.

To assess whether a family history of blood clots should play a role when establishing a patient’s blood clot-prevention regimen, researchers at Karolinska University Hospital in Stockholm studied the influence of family history on the risk of developing a blood clot in myeloma patients and in healthy individuals.

The study included data from all Swedish multiple myeloma patients (21,067) diagnosed between 1964 and 2004 and 83,094 healthy individuals who matched the patient pool in terms of sex, age, and geography. Additionally, researchers obtained data on 19,137 and 76,816 first-degree relatives (parents, siblings, and children) of these patients and healthy individuals, respectively.

Among the myeloma patients, 6.8 percent developed a blood clot, and 8.5 percent of those had a family history of blood clots. The myeloma patients with a family history of clots were 2.2 times more likely to develop blood clots than myeloma patients without a family history.

Comparatively, 6 percent of individuals in the general population developed blood clots, and of those, 6.3 percent had a family history. Those with a family history of blood clots were 1.5 times more likely to develop the condition than individuals without a family history.

For more information, please see the study in the Journal of Thrombosis and Haemostasis (abstract).