These authors analyzed data from Sweden's National Prostate Cancer Register, which includes 96 percent of all prostate cancer cases in that country. Men were divided into three groups: those receiving endocrine or hormone therapy to reduce levels of male hormones (including testosterone), those receiving surgery and/or radiation and those who were simply being watched.
Men taking hormone therapy had a 2.48 increased risk of developing a blood clot and almost double the chance of a pulmonary embolism (when the clot travels to the lung), compared to men without prostate cancer.
Those in the prostatectomy group had a 73 percent increased risk of blood clots and double the risk of a pulmonary embolism. Those in the "watch-and-wait group had a 27 percent increased risk of blood clots and a 57 percent increased risk of that clot moving to the lung.
None of the groups saw an increased risk of arterial embolism, when clots block an artery.
Those under the age of 65 and those with more advanced disease had even more risk. Given that men in the no-treatment-yet group also had more blood clots, much of the risk was likely from the cancer itself.
"This is probably telling us that something about the cancer and its biology may be impacting coagulation," Clinton said.
However, the type of treatment obviously also plays a role.
Still, the absolute number of blood clots seen in the study was relatively low -- about four per 1,000 person-years, up from 2.
"One should be aware of [the increased risk] and make sure that that the patient is being monitoring for symptoms of blood clots but you're not going to go so far as to recommend that we give [blood thinners] to everybody to prevent it," Clinton said.
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