Cancer-prevention studies in limbo

Drugs' risks may lead to cessation of clinical trials

April 29, 2005|By Shari Roan | Shari Roan,LOS ANGELES TIMES

The discovery that the painkillers Vioxx and Celebrex may increase the risk of heart problems wasn't just a disappointment to people with chronic pain and the doctors who treat them. The news has threatened to cut off a promising arm of research in cancer prevention.

For the last decade, scientists have been compiling evidence that those and other nonsteroidal anti-inflammatory drugs seem to interfere with the early processes that can give rise to cancer, particularly cancers of the digestive tract. Now, as many as 50 clinical trials are in limbo, say researchers who gathered last week in Anaheim, Calif., for the annual meeting of the American Association for Cancer Research.

Those trials have been testing not only the newer drugs - the so-called Cox-2 inhibitors - but also over-the-counter cousins such as aspirin and ibuprofen.

"NSAIDs have been agents that have been of great interest" to cancer researchers, said Dr. Robert Bresalier, chairman of the department of gastrointestinal medicine and nutrition at M.D. Anderson Cancer Center in Houston. "But I think we need to consider the question of risk versus benefit."

Research presented at the convention underscored the balancing act that researchers and doctors face when recommending nonsteroidal medications in "chemoprevention" - defined as the use of natural or synthetic substances to reduce the risk of cancer.

Norwegian scientists presented data showing that aspirin, ibuprofen, naproxen and three other traditional NSAIDs help smokers cut their risk of oral cancer by half. (Oral cancer is fatal within five years in about 50 percent of people who develop the disease.) But smokers taking the drugs did not have lower death rates overall - probably because they were experiencing more cardiovascular problems from the therapy, said Dr. Jon Sudbo, the lead author of the study from the Norwegian Radium Hospital in Oslo.

"This really raises a question of safety in cancer-prevention treatment," Sudbo said.

The discovery of a potential cardiovascular risk comes at a time when nonsteroidals have moved into the forefront of chemoprevention research. Years of animal studies and observational studies showed the drugs seemed to prevent cancer. Dozens of studies funded by the National Cancer Institute are, or were, under way to examine the drugs' effects on several types of cancer, including colon, breast, bladder, lung and prostate.

Approved for people with arthritis and other chronic pain conditions, the newer nonsteroidal drugs known as Cox-2 inhibitors came under scrutiny last year when studies showed a higher rate of heart attack, stroke and cardiovascular deaths among people taking the drugs.

Cox-2 inhibitors block cyclooxygenase enzymes, which are produced in response to inflammation and by precancerous and cancerous tissues. Unlike traditional nonsteroidal drugs, they are less likely to cause stomach bleeding when taken for extended periods of time. Vioxx and Bextra have since been taken off the market but Celebrex remains.

Some studies have also suggested that long-term use of the traditional nonsteroidal drugs may increase cardiovascular risk, and Sudbo's study is an early indication that all such drugs may raise risk.

Much of the early success using Cox-2 inhibitors has been in preventing the polyps that can lead to colon cancer. Scientists from the National Cancer Institute presented a study at last week's conference showing that Celebrex alters a specific set of genes in the colons of patients at high risk for a hereditary form of colon cancer, which may suppress the formation of colon polyps.

Researchers from Rutgers University showed that low doses of Celebrex and the cholesterol drug Lipitor taken together were more effective at limiting colon cancer in lab animals than higher doses of the drugs given separately. But future research is in peril.

One large clinical trial of Celebrex to reduce the occurrence of precancerous colon polyps was halted in December after investigators discovered the risk of heart attack, stroke and cardiovascular death was 2.5 times higher for people taking the drug than for people taking a placebo. Several chemoprevention studies using Vioxx were also halted last year, and the future of smaller studies involving Celebrex is unclear.

The Los Angeles Times is a Tribune Publishing newspaper.

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