Celebrex, a treatment for arthritis, may help prevent colon cancer in high-risk patients, but it also raises the risk of heart attack and stroke, researchers said on Monday.

Pfizer Inc. said sustained, higher doses of Celebrex can reduce pre-cancerous polyps by as much as 45 percent, based on the drug’s overall performance in two clinical trials.

However, a broad analysis of both studies found patients taking Celebrex had more cardiovascular events, contradicting a preliminary analysis of one of the studies.

Celebrex, a so-called COX-2 inhibitor, belongs to the same class of drugs as Merck & Co. Inc.‘s Vioxx, which Merck pulled from the market in 2004 after a study showed it doubled the risk of heart attack and stroke.

The studies, presented on Monday at the annual meeting of the American Association for Cancer Research, evaluated whether the over-expression of the COX-2 enzyme is related to the growth and spread of colorectal tumors.

COX-2 inhibitors may reduce the occurrence of the precursor, colorectal adenomas (benign tumors), in patients with a family history of the disease, as well as the development of sporadic colorectal tumors.

Both trials enrolled patients who had already had precancerous colon polyps removed. They were about 60 years old, on average, at the start of the trial; most had cardiovascular risk factors such as high blood pressure, diabetes, chest pain, previous heart attacks, strokes or were smokers.

One study, the APC trial, was co-sponsored by the National Cancer Institute and Pfizer. The other, the PreSAP trial, was sponsored by Pfizer.

Final results of the APC trial confirmed preliminary results from the study released in late 2004 showing a statistically significant increase in the risk of serious cardiovascular events in the Celebrex group compared to patients taking a dummy pill.

Pfizer said preliminary results of the PreSAP trial did not show an increase of cardiovascular events. But Pfizer said a new, broader analysis of cardiovascular events, including chest pain, found more cardiovascular events with Celebrex compared to placebo.

Pfizer said the results are consistent with the current warnings on cardiovascular risk in the Celebrex label.

The drugmaker said it has provided available information about the APC and PreSAP trials to regulatory agencies around the world. Pfizer said it will submit final study reports to the U.S. Food and Drug Administration and other regulatory agencies.