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NEW YORK (Reuters Health) - People who regularly take painkillers such as ibuprofen and naproxen may be at higher risk of kidney cancer, according to new research.
The findings suggest that the longer someone uses such drugs, called non-steroidal anti-inflammatories, or NSAIDs, the higher their risk of kidney cancer.
But they can't prove that painkiller use causes cancer, and the difference between regular users and non-users in the study was small. Researchers calculated that if there is a cause-and-effect relationship, about 10,000 people would have to take the drugs regularly for one additional person to get kidney cancer.
That doesn't mean people who need the drugs shouldn't take them, they said, especially because of their potential benefits on other types of cancer.
"NSAIDs have been associated with a reduced risk of several cancers, including colorectal, breast, and prostate," study author Eunyoung Cho, from Harvard Medical School in Boston, told Reuters Health. "The most important implication from our study is it raises the possibility that NSAIDs could increase the risk of certain kinds of cancer too."
The drugs have also been linked to an increased risk of stomach bleeding.
According to the National Cancer Institute, about 61,000 people in the U.S. will be diagnosed with kidney cancer in 2011, and about 13,000 will die of the disease.
The researchers took their data from two studies of about 125,000 nurses and other health professionals who filled out surveys every other year for up to two decades. Those surveys asked participants how often they took painkillers for arthritis and other conditions, and also tracked which people were diagnosed with kidney cancer.
In total, 333 people (about 0.3 percent) got kidney cancer. People who reported taking Tylenol or aspirin regularly (two or more times per week) were not more likely to be diagnosed with kidney cancer than those who didn't take painkillers.
However, participants who took NSAIDs other than aspirin, including ibuprofen (marketed as Advil) and naproxen (marketed as Aleve), were about 50 percent more likely than non-medication users to be diagnosed with the cancer.
The risk of kidney cancer was highest in people who took NSAIDs regularly for ten or more years.
Cho said that so far, researchers can't explain why aspirin wouldn't increase the risk of kidney cancer, but other NSAIDs might, because the drugs work in similar ways.
She and her colleagues were able to show that some measures of health, such as physical activity, diet, weight and smoking, didn't explain the link between painkiller use and kidney cancer.
They still can't exclude the possibility that something else is driving the association. But Cho said the fact that they saw the link in two different study populations makes her more confident that non-aspirin NSAIDs and kidney cancer really are related.
Joseph McLaughlin, a researcher from the International Epidemiology Institute in Rockville, Maryland, cautioned against making too much of the results.
"One can never draw any firm conclusions" from a study based on observation alone, he told Reuters Health, differentiating the research from a study in which some people are given painkillers and others are given placebo -- though that's not really feasible, he added.
The painkillers, said McLaughlin, who was not involved in the study, seem to be linked "in a few long-term users with a moderately increased risk. Whether that's causal or not, that remains to be seen."
So far, Cho agreed, the findings shouldn't drive anyone's decision about whether or not to take painkillers. "If our study is confirmed, risk and benefit should be considered when deciding whether to give (NSAIDs), especially for a long period of time," she concluded.
SOURCE: bit.ly/qPmJEI Archives of Internal Medicine, online September 12, 2011.