May 11, 2011

Frequent Acetaminophen Use Ups Blood Cancer Risk

Frequent users of acetaminophen are at a slightly increased risk for blood cancers, according to new research from scientists at Fred Hutchinson Cancer Research Center in Seattle, Washington.

Although increased, the risk remains low overall, and it's still unclear what role the drug plays in the increase.

Earlier research has shown that aspirin use might lower the odds of dying from colon cancer but increase the risk of bleeding ulcers. But for blood cancers, the picture has been less clear.

"Prior to this study there was very little evidence that aspirin reduces your risk of hematological cancers," Fred Hutchinson Cancer Research Center researcher Emily White told Reuters Health.

White, who worked on the new research, said it has been suggested that acetaminophen might increase the risk of cancers, but those studies were based on individual cases of blood cancer.

Studies of individual patients are considered as strong as the new one, which tracked a large population of healthy people over time.

"We have the first prospective study," said White.

Although, there is no proof that acetaminophen -- sold as Tylenol in the US and paracetamol in Europe -- causes cancer, and the new results need to be confirmed before they are used in any treatment decision.

For the new research, scientists followed nearly 65,000 older men and women in Washington State. At the start of the study, they asked participants about their use of painkillers over the past ten years and made sure that no one had cancer -- not including skin cancer.

Over a six year period, 577 people (less than one percent) developed a cancer involving the blood cells, including such cancers as lymphoma and myelodysplastic syndrome (MDS).

More than nine percent of those who developed one of these cancers used high amounts of acetaminophen, compared to only five percent of those who didn't get cancer.

After accounting for age, arthritis and family history of certain blood cancers, chronic acetaminophen users had nearly twice the risk of developing the disease.

"A person who is age 50 or older has about a one-percent risk in ten years of getting one of these cancers," said White. "Our study suggests that if you use acetaminophen at least four times a week for at least four years, that would increase the risk to about two percent."

Other painkillers, including aspirin and ibuprofen, were not linked to the risk of blood cancers.

Acetaminophen works very differently than other painkillers and so might be expected to have different effects on cancer, said Dr. Raymond DuBois, a cancer prevention expert at the University of Texas MD Anderson Cancer Center in Houston.

Still, "It was quite surprising to see that acetaminophen use increased the risk of" blood cancers, DuBois, who was not involved in the study, told Reuters Health by email.

White said it is too soon to make any recommendations based on the research, and that none of the painkillers are free from side effects. "Long-term use of any over the counter drug might have adverse effects," she said, adding that the benefits of painkillers have to be weighed against the risks of side-effects that come with their usage.

The results of the study were published May 9 in the Journal of Clinical Oncology.


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