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The risk, which the researchers termed "borderline significantly increased," is more pronounced in men and patients who take high doses of the drug, according to the study, which was published online April 8 in the journal Cancer.
"When prescribing amiodarone, doctors need to keep in mind that this medication may increase cancer risk," said lead author Dr. Vincent Yi-Fong Su, from the Taipei Veterans General Hospital. "We suggest that cancer events should be routinely reported in future amiodarone trials, and further observational research is necessary."
Patients taking the drug, however, shouldn't fear they'll get cancer, one expert said.
"Amiodarone is among the most effective antiarrhythmic medications available," said Dr. Gregg Fonarow, a spokesman for the American Heart Association and professor of cardiology at the University of California, Los Angeles. "Well-controlled clinical trials have not demonstrated a significant increase in cancer with use of this medication."
The current study, called an observational study, doesn't prove that amiodarone causes cancer, only that an association was found between people taking the drug and cancer.
Many risk factors for heart disease and arrhythmia are also risk factors for cancer, Fonarow said. The findings of this study comparing those treated with amiodarone to the general population are most likely explained by selection of patients and other factors that weren't taken into account, he said.
"These findings should not be a concern to patients taking amiodarone," Fonarow said.
Amiodarone (sold as Cordarone and Pacerone) is commonly prescribed to prevent life-threatening arrhythmias, such as ventricular tachycardia or ventricular fibrillation, both of which can lead to cardiac arrest.
Ventricular tachycardia is a very rapid beating of the upper chambers of the heart. When these chambers don't beat in the correct order, the condition is called ventricular fibrillation. These problems prevent blood from being pumped properly and can cause the heart to stop beating altogether.
Amiodarone breaks down slowly, so large amounts can remain in soft tissues when the drug is taken for a long time. This might explain its association with cancer, the researchers said. Earlier studies have shown an association between amiodarone and cancer risk, but this is the largest study to date to show a link, they noted.
For the study, Su's team followed more than 6,400 patients taking amiodarone for almost three years. Among these patients, 280 developed cancer.
Men taking high doses of the drug had a 46 percent higher chance of developing cancer than those who were neither male nor taking large doses. Anyone taking high doses had nearly twice the risk of cancer compared with people taking low doses, the researchers found.
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