The debate on whether the popular class of antihypertensive drugs, angiotensin receptor blockers (ARBs), may be associated with an increased risk for cancer has been reopened with the publication of a new meta-analysis.
The analysis found an increasing risk for cancer, and specifically lung cancer, with increasing cumulative exposure to these drugs.
The findings are reported in a study published online in PLOS ONE.
The author of this new meta-analysis is Ilke Sipahi, MD, a cardiologist from Acibadem University Medical School, Istanbul, who previously raised this issue in an initial meta-analysis published in 2010.
“The new meta-analysis is important because it is the first study to investigate whether there is a dose response in the association between ARBs and cancer,” Dr. Sipahi told this news organization.
“I found a clear signal of increased risk of cancer as exposure to ARBs increased, and the association started to become significant when the maximum dose was taken for 3 years,” he added.
Dr. Sipahi explained that in the first meta-analysis published in Lancet Oncology, he and his colleagues reported an increased cancer risk with ARBs based on observations from high-exposure trials – those that included higher doses of ARBs with a long duration of follow-up.
Following this publication, an investigation by the U.S. Food and Drug Administration refuted the risk, and a collaboration of ARB trial investigators also performed an analysis published in the Journal of Hypertension (2011. doi: 10.1097/HJH.0b013e328344a7de), which again did not show an increased risk for cancer with use of ARBs.
Dr. Sipahi claims that those analyses by the FDA and the ARB Trialists Collaboration, which were all trial-level meta-analyses, diluted the “high exposure” data (including higher doses taken for longer periods of time) with a large amount of other data on much lower exposures (lower doses and/or shorter time periods).
“The overall risk would then inevitably become nonsignificant. These analyses also did not look at different exposure levels,” he says.
“For cancer, the degree of exposure is obviously very important. The risk associated with smoking 2 or 3 cigarettes a day for a year is very different from that of smoking 2 packs a day for 40 years. The same principle applies to taking a medication,” Dr. Sipahi asserts.
From these latest data, he estimates that 120 patients needed to be treated with the maximal daily dose of an ARB for 4.7 years for one excess cancer diagnosis, and 464 patients needed to be treated for one excess lung cancer.
“Given that at least 200 million individuals are being treated with an ARB globally, approximately 1.7 million excess cancers (and 430,000 lung cancers) in 4.6 years could be potentially caused by this class of drugs,” he suggests.
For the current analysis, Dr. Sipahi used trial-level data taken from the paper by the ARB Trialists Collaboration and investigated the effect of exposure to ARBs – including both the dose taken and the length of treatment – on risk for cancer. He performed metaregression analyses that he says has not been done before.
“I mathematically quantitated the degree of exposure in each trial. And when the degree of exposure was correlated with risk of cancer, there was a significant association.”
The new meta-analysis includes 15 randomized controlled trials. The two coprimary outcomes were the relationship between cumulative exposure to ARBs and risk for all cancers combined and the relationship between cumulative exposure and risk for lung cancer.
In the trials, 74,021 patients were randomly assigned to an ARB, resulting in a total cumulative exposure of 172,389 person-years of exposure to daily high dose (or equivalent), and 61,197 patients were randomly assigned to control.
Results showed a highly significant correlation between the degree of cumulative exposure to ARBs and risk for all cancers combined (slope = 0.07; 95% confidence interval, 0.03-0.11; P < .001) and also lung cancer (slope = 0.16; 95% CI, 0.05-0.27; P = .003).
In trials where the cumulative exposure was greater than 3 years of exposure to daily high dose, there was a statistically significant increase in risk for all cancers combined (risk ratio, 1.11; 95% CI, 1.03-1.19; P = .006).
There was also a statistically significant increase in risk for lung cancers in trials where the cumulative exposure was greater than 2.5 years (RR, 1.21; 95% CI, 1.02-1.44; P = .03).
In trials with lower cumulative exposure to ARBs, there was no increased risk either for all cancers combined or lung cancer.
Dr. Sipahi reports that the cumulative exposure-risk relationship with ARBs was independent of background angiotensin-converting enzyme (ACE) inhibitor treatment or the type of control (placebo or nonplacebo control).
But he acknowledges that since this is a trial-level analysis, the effects of patient characteristics such as age and smoking status could not be examined because of lack of patient-level data.
Dr. Sipahi says he does not know the mechanism behind these findings, but he draws attention to the recent withdrawal of several thousand lots of ARB formulations because of the presence of potentially carcinogenic impurities that have been suggested to be a byproduct of ARB synthesis.
He also claims that unlike some other classes of antihypertensives, ARBs have not been shown to reduce the risk for MI, leading him to conclude that “other classes of antihypertensives with good safety and efficacy data (such as ACE-inhibitors, calcium-channel blockers or others) should become the preferred first-line agents in the treatment of hypertension.”
Dr. Sipahi wants the FDA to reinvestigate the issue of ARBs and cancer risk using individual patient data. “They already have the patient-level data from the trials. They should look at it more carefully and look at exposure levels and how they relate to cancer risk,” he said. “And the fact that there have been studies linking high ARB exposure levels to increased cancer risk should at least get a warning on the drug labels.”