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Apparently, baby aspirin interacts with the hormone therapy to elevate liver-function test levels. The end result is the man must stop potentially lifesaving hormone therapy.
The findings are contained in a letter published in the Dec. 27 issue of the New England Journal of Medicine.
Hormonal therapy, which involves reducing levels of male hormones called androgens, is a common treatment for prostate cancer, but it can raise the risk of a heart attack. So men who are older or have known coronary risk factors such as diabetes or smoking usually take baby aspirin while undergoing hormone therapy because aspirin helps prevent blood clots.
"Aspirin is being prescribed more widely for these men so we looked to see if there was any effect of aspirin on prostate cancer outcomes," said lead researcher Dr. Anthony V. D'Amico, chief of the division of genitourinary radiation oncology at Brigham & Women's Hospital and the Dana-Farber Cancer Institute, both in Boston.
The authors analyzed data on 206 men with localized prostate cancers who were already enrolled in a trial to compare radiation therapy alone with radiation therapy plus hormone therapy. The hormone therapy included six months of the anti-androgen flutamide.
Flutamide had a tendency to elevate results of liver-function tests. Although these elevations were benign, they meant hormonal therapy had to be stopped, at least temporarily, D'Amico explained.
Men who didn't complete six months of hormone therapy were 3.5 times more likely to die compared to men who got the full course of hormone therapy.
"It was sort of a paradoxical finding," D'Amico said. "Men who were taking aspirin were more likely to die of prostate cancer than those who were not, which didn't make sense at first."
But when the researchers delved deeper, they realized that the men who were taking aspirin were more likely to have to stop hormone therapy.
"Liver function is something you monitor" when undergoing hormone therapy, D'Amico explained. "When the tests elevate, you take the patient off of hormone therapy till the tests normalize, then you restart the therapy."
An explanation for this interaction comes from previous animal studies, D'Amico said. For rabbits that take aspirin while undergoing hormone therapy, that aspirin is magnified 100-fold in terms of how much gets into the blood. "That makes it a toxic dose of aspirin," he explained.
Although such a study can't establish a cause-and-effect association, it does appear likely, D'Amico said.
"If a man is taking baby aspirin just to prevent heart disease, we would ask the oncologist to ask the primary-care physician if he could come off the baby aspirin for the months while he's getting cancer therapy. If the aspirin is just for prevention, this is probably the simplest thing to do," he said. "But if the patient is on aspirin because he absolutely needs it, then they'd have to treat the prostate cancer without hormone therapy. It really comes down to a trade-off: How much do they need the aspirin versus how much do they need hormonal therapy, and there are alternative treatments for prostate cancer."
SOURCES: Anthony V. D'Amico, M.D., Ph.D., chief, division of genitourinary radiation oncology, Brigham & Women's Hospital and Dana-Farber Cancer Institute, Boston; Dec. 27, 2007, New England Journal of Medicine
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