Experts clash on ARBs’ potential link to cancer

Angiotensin-receptor blockers (ARBs) are a common treatment for high blood pressure, heart failure and other conditions, and have been shown to reduce incidences of cardiovascular events. However, some studies suggest these drugs may increase the rates of cancer, including a recent meta-analysis published in Lancet Oncology (2010;11[7]:627-636).

The meta-analysis, which pooled data from nine randomized controlled trials, found increased rates of cancer, but not everyone agrees with the findings. “The analysis was not definitive and it actually asks more questions than it gives answers,” says William B. White, MD, president-elect of the American Society of Hypertension (ASH), who was not associated with the study. “You have to be careful because this analysis is not really a comparison of one drug versus another.”

Other points of contention, according to White, are that the studies were not designed specifically to look at cancer rates, nor did they contain homogenous populations. Some studies, for example, evaluated patients with heart failure, some with hypertension and others with hypertension and vascular disease.

Lead author of the meta-analysis Ilke Sipahi, MD, of the University Hospitals Case Medical Center in Cleveland, counters White by saying that three trials in the analysis specifically examine cancer risk and its association with ARBs. And while the trial populations did differ, the majority of patients in the trials were in their upper 60s, were mostly white and the cohorts were “not that heterogeneous.” However, smoking status did vary from 9 to 21 percent across the trials.

White says that because lung cancer takes a “very long time to develop, it would be highly unlikely that a drug could actually either stimulate its growth or could cause cancer.” Sipahi acknowledges that cancer is a slow phenomenon, but it doesn’t always take 40 years to develop. “People get testicular cancer at age 10 and kids have brain tumors at age three. Perhaps these drugs are increasing the growth of pre-existing tumors and they become prominent and cause symptoms that end in the clinical diagnosis of cancer.”

White says the analysis “lacks clarity and it should not be emphasized in practice at this time.” He adds that ASH would not recommend that a patient stop taking ARBs or other anti-hypertension drugs because of these study findings. “Because data were pooled and not taken from individual cases, there could be underlying confounders that could cause the problem more than the actual drug itself,” explains White, adding that the data are not robust enough to be definitive.

However, Sipahi contends that these data are disconcerting. He found that to cause one excess cancer case, 105 patients would need to be treated with ARBs. Multiply that number by an estimated 10 million people in the U.S. taking ARBs and “you are potentially causing 100,000 excess cancers by preferring this medication over other medications,” he says.