Researchers who suspended a trial that used controversial pain relievers to try to prevent lung cancer said on Tuesday they were resuming it after studying the risks.

The team at the University of Texas M.D. Anderson Cancer Center in Houston has restarted a trial studying celecoxib, a COX-2 inhibitor drug sold by Pfizer Inc. under the brand name Celebrex.

The researchers suspended the trial last December at the request of Pfizer and the National Cancer Institute after studies revealed the COX-2 drugs could raise the risk of Heart attack and Stroke.

But FDA advisers recommended in February that Celebrex, which has been widely prescribed for arthritis sufferers, continue to be studied in the treatment and prevention of cancer.

“At this point, there is nothing available to deter lung cancer in smokers, even in those who have quit,” said Dr. Jonathan Kurie, who is leading the study.

“In looking at the data, we believe the potential benefit to the patient is greater than the risk and we have ample safeguards in place to monitor patients even more closely than they are now,” Kurie said in a statement.

Patients’ blood pressure and cholesterol levels will be tracked closely and volunteers will only get the drugs for six months, Kurie said. Anyone who has had a heart attack or stroke will be excluded from the study.

The COX-2 drugs were designed to be safer replacements for non-steroidal anti-inflammatory drugs, or NSAIDS, such as aspirin, ibuprofen and naproxen. NSAIDS can cause often deadly gastrointestinal bleeding and are blamed for 16,000 deaths a year in the United States.

But the COX-2 drugs were found to raise the risk of heart attacks and strokes. Two - Pfizer’s Bextra and Merck & Co.‘s Vioxx - have been pulled from the market.

Several studies have suggested the drugs may prevent cancer, perhaps by limiting inflammation, which is also how they work to reduce arthritis pain.

The COX-2 enzyme may control the synthesis of prostaglandins, compounds involved both in inflammation and in the creation of new blood vessels - including those that feed tumors.

“Lab studies have shown that COX-2 is expressed at a high level in lung cancer,” Kurie said. “They may be triggering inflammation, which we suspect plays a role in lung cancer.

Lung cancer is the biggest cancer killer in many countries. This year, 173,000 new cases of lung cancer will be diagnosed in the United States and 157,000 people died of the disease in 2004.