LONDON (AP) — Men with prostate cancer being treated with hormone therapy have a slightly higher risk of developing a blood clot, new research says.

Experts analyzed data on more than 30,000 Swedish men with prostate cancer who were receiving hormone treatment. Men without prostate cancer had about a one in 1,000 chance of getting a blood clot. In men with prostate cancer on hormone treatment, researchers said that risk increased to about four in 1,000. The research was published online on Wednesday in the British medical journal, Lancet Oncology.

Hormone treatment is given to men with advanced prostate cancer and there are no real alternatives.

"It's a matter of doctors asking the right questions to monitor this risk," said Mieke Van Hemelrijck, of King's College London, and the paper's lead author.

Experts aren't sure why hormone therapy may be linked to blood clots, but suspect it is connected to testosterone. Testosterone is thought to protect the heart, and hormone therapy stops its production. With less testosterone, men might be more susceptible to developing a clot if the heart isn't pumping as well.

Because the chance of developing blood clots increases with age, cancer and its treatment, Van Hemelrijck said it was hard to tease out which factor was the most important.

"This should not change how patients are treated," said Dr. Philip Saylor of Massachussetts General Hospital, who was not linked to the study. He said more research was needed before rethinking treatment regimes for patients.