MONDAY, Sept. 12 (HealthDay News) -- The long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as Advil, Motrin and Aleve may slightly increase the risk for developing kidney cancer, Harvard researchers report.

Millions of people use these drugs regularly for pain and they have been associated with reducing the risk of some cancers, the researchers added.

"NSAIDs have been associated with a reduced risk of several types of cancer, including colorectal, breast and prostate," said lead researcher Eunyoung Cho, an assistant professor of medicine at Brigham and Women's Hospital and Harvard Medical School. "Our study raises a contradicting possibility that non-aspirin NSAIDs may elevate the risk of certain types of cancer."

"If our studies are confirmed, risks and benefits should be considered in deciding whether to use analgesics, especially for long duration," she added.

The report was published in the Sept. 12 issue of the Archives of Internal Medicine.

The researchers began the study because there was some epidemiological evidence, mainly from small case-control studies, of a link between the prolonged use of analgesics (pain-relieving medicines) and kidney cancer.

For the study, Cho's team collected data on 77,525 women and 49,403 men who took part in the Nurses' Health Study and the Health Professionals Follow-up Study. Among these individuals, the researchers looked for an association between kidney cancer and the use of different types of pain-relievers.

Specifically, they looked at the incidence of renal cell cancer, which accounts for about 85 percent of all kidney cancers. They also looked for other risk factors for kidney cancer, such as weight, smoking, physical activity and high blood pressure.

Over 16 years of follow-up for the women and 20 years for the men, there were 333 cases of renal cell cancer.

Although there was no association found between the risk for renal cell cancer and aspirin and acetaminophen use, there was an increased between regular use of non-aspirin NSAIDs and renal cell cancer. That resulted in a 51 percent increase in the relative risk of developing the condition, the researchers noted.

In addition, the risk was 19 percent lower if these drugs were used for less than four years. For those who used non-aspirin NSAIDs regularly for four to 10 years the risk for renal cell cancer increased 36 percent and went up almost three times for those who used these drugs regularly for 10 years or more, Cho's group found.

Eric Jacobs, strategic director of pharmacoepidemiology at the American Cancer Society, said that "this well-designed study adds to the evidence that long-term regular use of non-aspirin NSAIDs, such as ibuprofen or naproxen, may modestly increase risk of kidney cancer."

To put the result into perspective, kidney cancer is not especially common and all pain relievers have potential risks that need to be considered, he said. "Two important causes of kidney cancer are obesity and smoking, so maintaining a healthy weight and not smoking will greatly reduce risk of developing this cancer," Jacobs added.

Another expert, Dr. Matthew Galsky, an assistant professor of medicine, hematology, medical oncology and urology at Mount Sinai Medical Center in New York City, doesn't think most people taking NSAIDs have to worry.

"The absolute risk is really on the small side. It's nine to 10 per 100,000 person years," he said. "So many patients take these medications and so many benefit from them; the risk is really on the small side."

Most patients taking NSAIDs don't need to worry, Galsky said. "For the average user of non-aspirin NSAIDs the risk is not of significance; for the person taking these medicines daily for over 10 years, it is food for thought," he said.

More information

For more on kidney cancer, visit the U.S. National Library of Medicine.