Older men who opt for hormone-blocking therapy to treat prostate cancer might be slightly raising their risk of developing cataracts, hints new research.
However, it is not yet clear if the therapy does actually cause the clouding that develops in the lens of the eye.
The male hormone testosterone helps drive the growth of prostate cancer. So-called "androgen deprivation therapy," or ADT, suppresses production of testosterone. An estimated one of every three men with prostate cancer undergoes ADT, either in the form of drugs, such as Lupron or Zoladex, or surgery to remove the testicles.
Yet, it is increasing being recognized that ADT carries serious potential risks - namely, diabetes and obesity.
In October, the U.S. Food and Drug Administration ruled that certain hormone treatments for prostate cancer, including Lupron, Zoladex, Trelstar, and Eligard, must carry new warnings about an increased risk of diabetes and heart problems.
Because both obesity and diabetes have been linked to cataracts, "we suspected that cataract might have been another unintended consequence" of ADT, Jennifer Beebe-Dimmer of the Karmanos Cancer Institute in Detroit, Michigan, told Reuters Health in an e-mail.
To test their hunch, Beebe-Dimmer and her colleagues studied nearly 66,000 prostate cancer patients aged 66 or older from a large US cancer registry.
In this group, nearly half of the patients had received some form of ADT within the first six months of their diagnosis, mostly in the form of hormone-altering drugs.
Overall, about 111 new cataracts were diagnosed for every 1,000 men studied per year, report the researchers in the Annals of Epidemiology.
After accounting for other risk factors for cataracts, they found that men treated with the hormone drugs had, on average, a 9 percent increased risk of developing a cataract compared to those not treated with ADT. The risk rose by around 26 percent for the far smaller proportion of men who had their testicles removed.
The effect was strongest among men with no prior history of cataracts.
The increased risk is relatively small, noted Beebe-Dimmer. However, because so many men use ADT, she and her team estimate that about 5 percent of cataract cases in men with prostate cancer might be blamed on the therapy.
"With ADT so commonly used as part of a patient's treatment for prostate cancer, it's important to have a complete understanding of the negative consequences of therapy," Beebe-Dimmer said.
"Patients should be monitored carefully while on ADT for new diagnoses of diabetes, and potentially cataract," she added.
Cataracts affect more than 20 million Americans aged 40 or older and account for the majority of vision-related Medicare expenses.