The results of a recent Swedish study indicate that the development of blood clots in the veins or arteries of multiple myeloma patients negatively affects survival outcomes.

The study investigators conclude that these findings warrant further studies to determine whether blood clot prevention measures can extend the survival of myeloma patients.

“There are effective ways to prevent venous and arterial thrombosis in myeloma patients; e.g, aspirin, heparin, warfarin (Coumadin), and Pradaxa (dabigatran),” said Dr. Edward Libby of the University of Washington School of Medicine in Seattle, who was not involved with the study. “Hopefully this important and well-conducted study will shed light on the topic and contribute to a decrease in the frequency of this preventable and potentially catastrophic complication in myeloma patients.”

Previous studies have shown that multiple myeloma patients are at risk of developing blood clots in the veins, called venous thromboembolism. Patients treated with Revlimid (lenalidomide) or thalidomide (Thalomid) in combination with dexamethasone (Decadron) are at an even greater risk of developing blood clots (see related Beacon news).

Whether blood clots affect the survival of myeloma patients remains unclear because the results of the current study contradict those of three previous smaller retrospective studies designed to examine this issue. All three previous studies reported no significant differences in survival outcomes between patients with and without venous blood clots.

The researchers note important differences in the studies that may have contributed to the varying results.

First, the current study included patients diagnosed with multiple myeloma within one particular population and followed them for a long period of time.  In contrast, prior analyses used data from clinical trials that excluded patients with poor overall health or focused on relapsed and/or refractory patients who have a lower risk of developing blood clots compared to newly diagnosed patients.

Additionally, the patients included in the current study (median age 71 years) were older than those in previous studies (57 years and 63 years).

Lastly, the majority of patients in the current study were not treated with thalidomide and very few were treated with Revlimid because these agents were not yet available during a large portion of the study period.

The current study included data from 9,399 Swedish multiple myeloma patients who were diagnosed between 1987 and 2005.

Among the myeloma patients included in the study, 724 developed venous blood clots and 1,572 developed arterial blood clots after their myeloma diagnosis.

The study investigators found that myeloma patients who developed blood clots had poorer survival outcomes compared to patients who did not develop blood clots.

Those who developed venous blood clots had a 2.9-fold higher risk of death within one year of their myeloma diagnosis, a 1.6-fold risk within five years, and a 1.6-fold risk within 10 years, compared to patients who did not develop blood clots.

Patients who developed arterial blood clots had a 3.4-fold higher risk of death within one year after diagnosis, a 2.2-fold risk after five years, and a 2.1-fold risk after 10 years.

Since myeloma patients are at a higher risk of developing blood clots soon after diagnosis, the researchers specifically investigated the impact that blood clots soon after diagnosis have on survival.

The researchers found that patients who survived arterial blood clots that developed within the first six months of diagnosis had an increased risk of death at one year (1.5 fold), five years (1.4 fold), and 10 years (1.4 fold) compared to that of patients who did not develop blood clots. This was not the case for venous blood clots.  Patients who survived venous blood clots during the first six months after diagnosis had a risk of death that was similar at one year (1.4 fold), five years (1.1 fold), and 10 years (1.0 fold) to that of patients who did not develop blood clots.

Blood clots had a similar effect on the survival of those diagnosed before and those diagnosed after 2000 when thalidomide became available for use in Sweden.  This result confirms that blood clots in multiple myeloma patients remain a serious complication even with the incorporation of novel agents into current treatment regimens.

For more information, please see the study in the journal Haematologica (pdf).