Roche Holding AG's prescription diet drug Xenical should immediately be pulled from the U.S. market after recent data linked it to precancerous colon lesions in animal studies, a consumer group told federal health regulators.

In a petition, Public Citizen also asked the U.S. Food and Drug Administration to reject making the weight-loss pill widely available over the counter.

The FDA recently said it granted GlaxoSmithKline Plc. conditional approval to sell the drug without a prescription if it first meets certain undisclosed criteria. Glaxo owns U.S. rights for nonprescription sales of Xenical.

"The failure to ban the prescription version of this drug, or worse, to make it much more widely available by allowing OTC sales is a decision that is likely to increase cancer incidence," Public Citizen wrote.

The group said a December 2005 study confirmed earlier company data showing Xenical, known generically as orlistat, can cause abnormal cell growth in the lining of the colon. Experts widely recognize the lesions as an early indicator of cancer, the advocacy group added.

The study, published in the journal Cancer Letters, found "a significant increase" of colon lesions in rats given Xenical regardless of whether they were on high-fat or standard diets.

"This finding makes it even clearer how ill-advised switching orlistat to OTC status would be," the petition said.

Roche spokesman Terry Hurley did not have any specific comment on the petition, but said "the overwhelming body of evidence indicates Xenical is safe." Representatives of Glaxo did not respond to an e-mail seeking comment.

Xenical comes in 120-milligram capsules to be taken three times a day with meals. The proposed nonprescription version, called Alli, comes in 60 mg tablets with 1-2 taken with meals.

It works by preventing fat from being absorbed by the body but can cause excess gas, oily discharge and other gastrointestinal problems.

BREAST CANCER

Public Citizen also said its review of reported side effects after Xenical hit the market in 1999 found 28 cases of breast cancer in patients taking Xenical through June 2005.

A review of its rival, Abbott Laboratories Inc.'s appetite suppressant Meridia, found two breast cancer cases between November 1997 and June 2005.

The FDA was aware of the breast cancer risk as well as possible colon lesions when it initially considered Xenical, Public Citizen said, but the agency chose to rely on the company's analysis.

FDA spokeswoman Laura Alvey said the FDA would carefully review the petition before responding to it.

The link between fat and cancer is unclear, but some studies have shown a higher risk in people who are overweight or obese. Other studies have shown no change in risk despite lower fat diets.

Some early data have shown Xenical's key ingredient can help curb fatty acids and possibly limit tumor growth, Public Citizen said, and removing it from the market would not stop future research.

But "at this point, the evidence of orlistat's ability to cause cancer is much stronger than any potential ability to prevent it," the group said.

Glaxo shares rose 67 cents, or 1.3 percent, to $52.15 in New York after earlier gaining 1.15 percent in London. Roche shares closed up 1.3 percent on the Swiss market.