Treating hypertension with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) was associated with a reduced risk for colorectal cancer, according to findings from a large retrospective study.
However, another study reported just over a year ago suggested that ACE inhibitors, but not ARBs, are associated with an increased risk for lung cancer. An expert approached for comment emphasized that both studies are observational, and, as such, they only show an association, not causation.
In this latest study, published online July 6 in the journal Hypertension, the use of ACE inhibitors/ARBs was associated with a 22% lower risk for colorectal cancer developing within 3 years after a negative baseline colonoscopy.
This is the largest study to date, with a cohort of more than 185,000 patients, to suggest a significant protective effect for these two common antihypertensive medications, the authors note. The risk of developing colorectal cancer decreased with longer duration of ACE inhibitor/ARB use, with a 5% reduction in adjusted hazard ratio risk for each year of use. However, this effect was limited to patients who had negative colonoscopies within a 3-year period and did not extend beyond that point.
Lead author Wai K. Leung, MD, clinical professor of medicine at the University of Hong Kong, explained that they are not advising patients to take ACE inhibitors simply to prevent cancer. “Unlike aspirin and statins, the potential chemopreventive role of ACE inhibitors on cancer has never been established,” he said in an interview. “The study findings may favor the use of ACE inhibitors in the treatment of hypertension, over many other antihypertensives, in some patients for preventing colorectal cancer.”
Increased or reduced risk?
There has been considerable debate about the potential carcinogenic effects of ACE inhibitors and ARBs, and the relationship with “various solid organ cancer risks have been unsettled,” the authors note. Studies have produced conflicting results – showing no overall cancer risk and a modestly increased overall cancer risk – associated with these agents.
A recent study reported that ACE inhibitors, as compared with ARBs, increased risk for lung cancer by 14%. The risk for lung cancer increased by 22% among those using ACE inhibitors for 5 years, and the risk peaked at 31% for patients who took ACE inhibitors for 10 years or longer.
The lead author of that lung cancer study,, of McGill University in Montreal, offered some thoughts on the seemingly conflicting data now being reported showing a reduction in the risk of colorectal cancer.
“In a nutshell, this study has important methodologic issues that can explain the observed findings,” he said in an interview.
Dr. Azoulay pointed out that, in the univariate model, the use of ACE inhibitors/ARBs was associated with a 26% increased risk of colorectal cancer. “It is only after propensity score adjustment that the effect estimate reversed in the protective direction,” he pointed out. “However, the variables included in the propensity score model were measured in the same time window as the exposure, which can lead to an overadjustment bias and generate spurious findings.”
Another issue is that the study period did not begin at the time of the exposure, but rather at a distant point after treatment initiation – in this case, colorectal cancer screening. “As such, the authors excluded patients who were previously diagnosed with colorectal cancer prior to that point, which likely included patients exposed to ACE inhibitors/ARBs,” he said. “This approach can lead to the inclusion of the ‘survivors’ for whom the risk of developing colorectal cancer is lower.
“But certainly,” Dr. Azoulay added, “this possible association should be investigated using methodologically sound approaches.”