TUESDAY, May 10 (HealthDay News) -- Those who take acetaminophen -- best known as Tylenol -- regularly for some time might be putting themselves at an increased risk for developing certain blood cancers, University of Washington researchers report.
The results of earlier studies looking at the association between over-the-counter painkillers or nonsteroidal anti-inflammatory drugs (NSAIDs) and blood cancers have been mixed, but this study suggests a risk tied to acetaminophen, the scientists noted.
"We found that high use of acetaminophen, one of the most frequently used medications worldwide, was associated with an almost twofold increased risk of incident hematologic malignancies," said lead researcher Dr. Roland Walter, an assistant professor of medicine in the division of hematology.
The report was published in the May 9 online edition of the Journal of Clinical Oncology.
While the research found a potential association between acetaminophen use and blood cancers, it did not prove a cause-and-effect. And several experts called for follow-up studies.
For the study, Walter's team collected data on 64,839 men and women aged 50 to 76, who took part in the Vitamins and Lifestyle (VITAL) study. Among these individuals, the researchers identified 577 cases of blood cancers.
The researchers found that those who used acetaminophen at least four days a week over four years had almost a twofold increased risk for some blood cancers. These cancers included: myeloid neoplasms, non-Hodgkin lymphomas and plasma cell disorders.
However, acetaminophen use was not associated with an increased risk for chronic lymphocytic leukemia/small lymphocytic lymphoma, Walter's group noted.
This risk was not seen with the heavy use of other painkillers such as aspirin, other NSAIDs or ibuprofen, the researchers said. However, there was also no association between other painkillers and decreased risk, implying that these drugs are unlikely to be useful for prevention of blood cancers, Walter noted.
"Acetaminophen use on the majority of the days over many years appears to be associated with this new adverse effect," Walter said. "However, the study does not allow one to conclude a causal relationship," he added.
According to the researchers, animal studies have linked acetaminophen to toxic effects on bone marrow, which could be why there is a greater risk for blood cancers with long-term use of the drug.
Bonnie Jacobs, a spokeswoman for McNeil Consumer Healthcare, a division of McNeil-PPC, Inc., the maker of Tylenol, noted that "Tylenol has over 50 years of clinical history to support its safety and efficacy."
She added, "We appreciate the assessment of the authors that further studies would be needed before it is possible to draw any conclusions about the use of acetaminophen, and we welcome additional research in this area."
Walter noted that the risk of blood cancers is relatively small; an estimated combined total of 137,260 people in the United States were diagnosed with leukemia, lymphoma or myeloma in 2010. "New cases of leukemia, lymphoma and myeloma are expected to account for 9 percent of the new cancer cases diagnosed, so even a doubling of that risk is still relatively small," he said.
Deborah Banker, vice president of research communications at the Leukemia & Lymphoma Society, said that "it is unclear why chronic lymphocytic leukemia/small lymphocytic lymphoma should have different risk associations with acetaminophen use."
Eric Jacobs, strategic director of pharmacoepidemiology at the American Cancer Society, said that "there is no evidence from this study that less frequent or shorter-term use might raise risk of these cancers. Replication of this finding in additional high-quality studies is needed."
For more information on blood cancer, visit the Leukemia & Lymphoma Society.
SOURCES: Roland Walter, M.D., Ph.D., assistant professor, medicine, division of hematology, University of Washington School of Medicine, Seattle; Deborah Banker, Ph.D., vice president, research communications, Leukemia & Lymphoma Society; Eric Jacobs, Ph.D., strategic director, pharmacoepidemiology, American Cancer Society; Bonnie Jacobs, spokeswoman, McNeil Consumer Healthcare Division, McNeil-PPC, Inc.; May 9, 2011, Journal of Clinical Oncology, online
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