They said an analysis of available data on drugs in the class known as angiotensin-receptor blockers showed patients were 1.2 percent more likely to be diagnosed with a new cancer over four years than others who did not take the drugs.
Most patients in the trials (86 percent) took German drugmaker Boehringer Ingelheim's telmisartan, sold as Micardis, which has annual sales of more than $1.5 billion.
The increased risk of new cancer occurrence is modest but significant, Dr. Ilke Sipahi and colleagues from Case Western Reserve University in Cleveland and colleagues wrote in the journal Lancet Oncology.
There were not enough data in the studies to say if individual drugs in the class raise the risk or if it is a so-called class effect shared by all such drugs.
Even so, Dr. Steven Nissen, a cardiologist at the Cleveland Clinic, said in a commentary the findings were disturbing and provocative, raising crucial drug safety questions for practitioners and the regulatory community.
He said regulators need to look more closely at the risk of cancer with ARB use and that doctors should be more cautious about prescribing ARBs, and especially Micardis.
Privately held Boehringer Ingelheim defended the safety of its drug, saying in a statement its own internal safety data analysis of primary data contradicts the conclusions of an increased cancer risk.
Nissen did a similar analysis that raised alarms about heart risks from GlaxoSmithKline diabetes drug Avandia.
Currently, there are no major safety concerns linked with taking angiotensin-receptor blockers or ARBs, which work by blocking receptors for angiotensin II, a hormone that increases blood pressure.
But a 2003 study in patients with heart failure did find that the drug Atacand, or candesartan, made by the Anglo-Swedish firm AstraZeneca, significantly raised the risk of fatal cancers compared with a dummy pill.
PUBLICLY AVAILABLE DATA
Sipahi and colleagues did a so-called meta-analysis, pooling all publicly available data from randomized trials of ARBs published before November 2009.
Other drugs in the class include Merck & Co's Cozaar, sold generically as losartan; Diovan or valsartan made by Swiss drug firm Novartis; irbesartan, jointly marketed by Sanofi-Aventi and Bristol-Myers Squibb as Avapro; Daiichi Sankyo's Benicar or olmesartan; and Solvay Pharmaceuticals' Teveten or eprosartan.
Overall, they found that patients taking the drugs had 7.2 percent risk of having a new cancer diagnosis, compared with 6 percent risk for patients in the control groups.
When they looked at cancer types, only lung cancer stood out, with 0.9 percent of patients taking blood pressure drugs developing a new lung cancer compared with 0.7 percent of patients in the control arm.
The drugs did not appear to increase the risk of death from cancer, but the team said cancers can develop slowly and cancer deaths might not show up in the relatively short studies.
Just three out of seven FDA-approved drugs -- telmisartan, losartan, and candesartan -- were studied, and it is not clear what affect other drugs in the class might have on cancers.
Nevertheless, they said given how widely the drugs are used, the risk is worth further study.
Boehringer Ingelheim said its own analysis of data from three large trials showed no increased cancer risk associated with Micardis. But in one study, called ONTARGET, there was a slight increased risk in one treatment arm when the drug was taken in combination with common blood pressure drugs known as ACE-inhibitors, such as ramipril.
The company said the product label does not recommend the drug be used in combination with ACE-inhibitors.
Nissen said the study is limited by the fact that the trials were not designed to look at cancer risks.
But he said the drugs are often overprescribed because of aggressive marketing, and patients might fare just as well taking inexpensive ACE inhibitors instead.
Other experts stressed that patients need to keep taking their blood pressure medications.
At the moment there isn't enough evidence to draw any firm conclusions about how blood pressure drugs might affect cancer risk and this will need further investigation, Martin Ledwick, head information nurse at Cancer Research UK, said in a statement.