However, most COX-2 inhibitors ran into safety issues a few years after their approval, and now only Celebrex remains on the U.S. market. At a cost of several dollars per day, depending on dosage, it is much more expensive than older pain relievers such as ibuprofen.

During the study, Dr. Nadir Arber of Tel Aviv University and his colleagues reviewed data collected from 1,561 people with a history of colorectal cancer. More than half had received Celebrex for approximately 3 years, before concerns over the increased risk of cardiovascular problems caused researchers to discontinue the study.

The scientists then followed the people willing to continue the research for another 2 years, noting who developed new polyps, including advanced polyps with features that suggest they’re more likely to become cancerous. Approximately half of the people who started the study agreed to continue.

Not surprisingly, Celebrex users were more likely to develop cardiovascular problems, including a 66 percent higher risk of serious cardiac disorders. But over the total 5-year period, people who took Celebrex were also less likely to develop new and advanced polyps than people who took a placebo.

Specifically, new polyps were found in 58 percent of people on placebo, and only 51 percent on Celebrex.

However, during the 5th year of the study alone, after the trial had been over for 2 years, 27 percent of Celebrex users developed new polyps, versus only 16 percent of people who had been on placebo - translating to a 66 percent higher risk among those who previously took Celebrex. Those who had been on Celebrex were also more likely to develop advanced polyps during that final year.

This rebound in risk actually makes biological sense, Chan told Reuters Health. If COX-2 inhibitors protect against colon cancer by blocking an enzyme pathway, when that blockage is released, the disease could occur “potentially at higher levels than had you never been on the drug in the first place,” he said.

Still, the results are “very promising,” Arber told Reuters Health by e-mail, adding he is now working to identify people who could benefit from the drug without experiencing the side effects.

Only half of the people who originally agreed to participate in the study remained after 5 years, and it’s unclear how this might affect the results, noted Chan, whose own research suggests aspirin could prevent deaths from colorectal cancer.

However, for a study that lasts this long, “those are acceptable numbers,” noted Arber.

If patients asked him whether they should take celecoxib to prevent colorectal cancer, Arber would tell them “no,” he added. “They should speak with their doctor.”

SOURCE: The American Journal of Gastroenterology, online April 19, 2011.