Androgen deprivation therapy (ADT) in men with prostate cancer is associated with an increased risk of thromboembolic disease (TED), and this risk may increase with duration of therapy, according to a new study.

Sean O’Farrell, a PhD student at King’s College London, and colleagues assessed TED risk among 42,263 men with prostate cancer (PCa) receiving ADT compared with a matched cohort of 190,930 men without PCa. The researchers looked specifically at the relationship between ADT and deep vein thrombosis (DVT) or pulmonary embolism (PE).

Relative to the comparison cohort, PCa patients treated with gonadotropin-releasing hormone (GnRH) agonists or surgically castrated patients had a 67% and 61% increased risk of TED, respectively, O’Farrell and his colleagues reported online ahead of print in BJU International. Men on anti-androgen monotherapy had a 51% decreased risk for DVT.

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Men who switched from anti-androgen therapy to GnRH agonists had the greatest risk for TED, according to the researchers. Compared with the matched cohort, PCa patients who made the switch had a 2.5 times increased risk for both DVT and PE after adjusting for confounders, including previous surgeries and proxies of disease progression. The risk increased with GnRH agonist exposure. For DVT, the risk was increased nearly 4-fold during the first year on GnRH agonist treatment and 4.5-fold after 2 or more years on the treatment. For PE, the risk was increased 2.2-fold during the first year, 3.5-fold during years 1–2, and 4.4-fold for exposure of 2 years or more.

“These findings support the theory that only men with a relevant indication should receive systemic ADT, to minimize thromboembolic side effects,” the authors concluded.