About 85 percent of those people were on telmisartan, sold as Micardis, made by Boehringer Ingelheim Corp. There was no difference in the rate of cancer deaths in people on the drugs compared to those not on them.

The study was published Monday in the medical journal, Lancet Oncology. No funding was provided for the study, but Dr. Ilke Sipahi, the study's lead author, has received past payments from drug makers Pfizer Inc., AstraZeneca PLC and Ranbaxy Pharmaceuticals Inc., which all make blood pressure drugs. Other authors reported similar grants from other pharmaceuticals.

"The risk for the individual patient is modest," said Sipahi, associate director of heart failure and transplantation at University Hospitals Case Medical Center in Cleveland. "However, when you look at it from the population level, millions and millions of people are on these drugs and it can cause a lot of excess cancer worldwide."

Don't stop medication
Sipahi warned patients not to stop taking their drugs, and recommended they consult their doctor if they were concerned.

Since completing the analysis, Sipahi said he now thinks twice about whether to prescribe the drugs. But he said many heart patients couldn't take other drugs because of their side effects and they should continue taking ARBs since their chances of dying from heart failure outweighed their chances of getting cancer.

Scientists aren't sure why ARBs might raise the possibility of developing cancer, though some animal studies suggest the medications help produce new blood vessels, which would speed tumor growth.

In an accompanying commentary in the Lancet Oncology, Steven Nissen, a cardiologist at the Cleveland Clinic, described the study as "disturbing and provocative." He called for regulatory agencies to order drug makers to submit more data on their products and to promptly report their findings.

Michael Thun, vice-president emeritus of epidemiology and surveillance at the American Cancer Society, said the study underlined how hard it is to pick up potentially dangerous side effects in drugs once they are on the market. He was not connected to the study.

Sipahi and colleagues calculated that one extra cancer case will occur for every 105 people taking the medications for about four years. He said there wasn't enough information to know if this increased cancer risk disappears once people stop taking the medications.

The maker of the most-used drug in the study, Boehringer Ingelheim, disputed the findings and said Micardis is one of the best-researched drugs worldwide. The company claimed in a statement that it had "internal safety data" contradicting the Lancet study. According to studies run by the pharmaceutical, there was no link between increased cancer risk and Micardis.

• MSNBC News