Clot risk in prostate cancer

Behind the Headlines

Thursday April 15 2010

Every year in the UK, 1 person in 1,000 develops DVT

“Prostate cancer patients have double the risk of suffering blood clots which can lead to DVT,” the Daily Mail reported. It said that the risk of DTV (deep vein thrombosis) is greatest for men undergoing hormone therapy for prostate cancer and in younger men with advanced-stage cancer.

This large study in 76,000 Swedish men looked at the rates of thromboembolic diseases, which include DVT and pulmonary embolism (PE), and found that they occurred more often in men with prostate cancer than in the general population. The risk of these diseases varied according to which cancer treatment was used, with the highest risk in men who were primarily treated with hormone therapy. These men had about 2.5 times the rate of DVT and twice the rate of PE compared to the general male population.

Cancer and its various treatments have already been established as risk factors for thromboembolism, though the reasons for this are not clearly established. Though the rates of embolism differed according to cancer treatment in this study, it is not clear whether this difference in risk is due to the treatment itself or other physiological factors of the individual and their cancer that caused this treatment to be selected in the first place.

This research is valuable as it has studied a large population and made some progress in quantifying the size of the association between prostate cancer, different treatments and thromboembolism. It also highlights the need for men with prostate cancer and their doctors to be alert to possible symptoms of thromboembolism so that they can be quickly and effectively treated.

 

Where did the story come from?

This research was carried out by Mieke Van Hemelrijck from Kings College London and colleagues from institutions in Sweden. The study was funded by the Swedish Research Council, Stockholm Cancer Society and Cancer Research UK. The research was published in the peer-reviewed medical journal The Lancet.

 

What kind of research was this?

This cohort study examined the relationship between prostate cancer, how it is treated (hormone treatment, surgery or surveillance) and the risk of thromboembolism, such as DVT. A thromboembolic disease involves the formation of a blood clot (thrombus) in a blood vessel. The clot, or part of it, can break loose and become lodged in a blood vessel elsewhere, such as in the lungs (pulmonary embolism).

A large cohort study is one of the best ways to look at the incidence of adverse effects. However, the study needs to take into account confounding factors that may be associated with the exposure (cancer or its treatment) and the outcome (thromboembolism). Data from randomised controlled trials may provide additional information on the adverse effects of different treatments, but as thromboembolism is a relatively rare outcome, the numbers would probably be too small to provide accurate comparison. The fact that different treatments may be suited to different groups of men will also limit the comparability of these treatments in randomised controlled trials.

 

What did the research involve?

This research used a Swedish database (PCBaSe) based on the National Prostate Cancer Register. Since 1996, the PCBaSe has collected data on 96% of diagnosed prostate cancers. Information includes cancer stage at diagnosis and the initial treatment plan in the first six months following diagnosis. The database was also linked to other national registers to obtain socio-demographic data and information on hospital discharges and other medical illnesses. Various other sources were used to collect data on age at cancer diagnosis, prostate-specific antigen (PSA) levels, stage and grade of tumour, primary treatment, socio-demographic status, history of thromboembolism and date of death. Between January 1997 and December 2007, 30,642 men received primary hormone treatment, 26,432 were treated surgically and 19,526 were managed with a watch-and-wait approach.

The researchers analysed the relationship between prostate cancer, its treatment and thromboembolism (including DVT, PE and arterial embolism).

The researchers then calculated standardised incidence ratios (SIR) for thromboembolic disease using these data and comparing them to data on the general Swedish population. An SIR is an estimated ratio of how often a disease occurs in a given population compared to what might be expected in a larger “normal” comparison population. As the PCBaSe contains data on the general Swedish population, rates of thromboembolism in men with prostate cancer could be compared to expected rates in the general Swedish male population. These figures took into account the age of the men with prostate cancer and when they developed thromboembolism.

 

What were the basic results?

During the 10-year period, 1,881 men with prostate cancer developed a thromboembolic disease. The average follow-up time for each individual was three to four years.

The SIRs for thromboembolism of the men with prostate cancer compared to expected rates from a similarly aged Swedish male population were:

  • For men on hormone therapy, the SIR for DVT was 2.48 (over double the rate in the general Swedish male population) and the SIR for PE was 1.95. There was no difference in rates of arterial embolism (SIR 1.00).
  • For men who received surgical treatment, the SIR for DVT was 1.73 and the SIR for PE was 2.03. As with hormone therapy, there was no difference in rates of arterial embolism.
  • For men who were being managed with a watch-and-wait approach, the SIR for DVT was 1.27 and the SIR for PE was 1.57. There was no difference in rates of arterial embolism.
  • Subanalysis by age and tumour stage gave similar results.

 

How did the researchers interpret the results?

The researchers concluded that men with prostate cancer are at increased risk of thromboembolic diseases and those receiving hormone therapy have the highest risk. They say that these results “indicate that prostate cancer itself, prostate cancer treatments, and selection mechanisms all contribute to increased risk of thromboembolic disease”.

 

Conclusion

This large study looked at the rates of thromboembolic diseases, such as DVT and PE, in 76,600 men diagnosed with prostate cancer in Sweden. The researchers found that the men with prostate cancer had a higher rate of DVT and PE compared to men in the general population. Rates were found to differ according to cancer treatment approach and were highest in men primarily treated with hormone therapy (about 2.5 times the rate of DVT and twice the rate of PE compared to the general male population).

The study has strengths, for example including a large number of people, but may have some limitation in that it relied on the accuracy and completeness of medical and database records. Also, though the rates of embolism differed by cancer treatment, it is not clear whether this difference in risk is due to the treatment itself, or due to the other physiological factors of the individual and their cancer that caused this treatment to be selected in the first place.

Cancer and its various treatments have already been established as risk factors for thromboembolism, though the underlying reasons for this are not firmly established This study is valuable as it has made some progress in quantifying the size of the association between prostate cancer, different treatments and thromboembolism. It also highlights the need for men with prostate cancer and their doctors to be alert to possible symptoms of thromboembolism so that they can be quickly and effectively treated.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Prostate cancer ‘increases the risk of blood clots’ new study showsThe Times, April 14 2010

Blood clot risk for men with prostate cancerThe Daily Telegraph, April 14 2010

How prostate cancer raises the risk of suffering blood clots which can lead to DVTDaily Mail, April 14 2010 

Links to the science

Van Hemelrijck M, Adolfsson J, Garmo H, et al. Risk of thromboembolic diseases in men with prostate cancer: results from the population-based PCBaSe Sweden. The Lancet Oncology, 14 April 2010 (early online publication)

 

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