The cholesterol treatment Crestor has been shown to partially reverse the build-up of plaque in coronary arteries, the first time that a statin drug has proved effective in treating the condition, which can lead to a heart attack or stroke, researchers said on Monday.

AstraZeneca Plc’s Crestor, in a two-year study of 507 patients, showed that intensive treatment reduced plaque volume by 7 percent to 9 percent. The drug also reduced levels of LDL, or “bad,” cholesterol by more than 53 percent and raised levels of HDL, or “good,” cholesterol by nearly 15 percent.

The changes in cholesterol levels were the largest ever seen a major trial of statin drugs, researchers said, who presented the results at a meeting of the American College of Cardiology in Atlanta.

“The results were shockingly positive,” said Dr. Steve Nissen, interim director of the department of cardiovascular medicine at the Cleveland Clinic and the study’s lead author.

He did note that the trial did not answer the question of whether the plaque reduction results in fewer heart attacks and strokes. But he said the study does indicate that very low LDL levels accompanied by raised HDL, can regress, or partially reverse, the plaque buildup in the coronary arteries.

Atherosclerosis results when a build-up of cholesterol, inflammatory cells and fibrous tissue form areas in the artery wall called plaques. If these plaques rupture, they can block blood flow to critical organs such as the heart or brain and can lead to heart attack or stroke.

Nissen said he doubted that plaque could be reduced by much more than the levels seen in the Crestor trial, which used the highest approved dose for the drug.

With the statin, “I think you get rid of the lipid, and what’s now left is the fibrous material, which won’t rupture,” he explained. “It’s a stable scar ... there is nothing to cause morbidity or mortality,” Nissen said.

Shares of AstraZeneca moved higher in London after the company announced general results from the trial. The shares were up 2.3 percent at 2954 pence on the London Stock Exchange, and were up 2.6 percent at $51.10 on the New York Stock Exchange.

Crestor, a key growth driver for the company, was initially estimated by industry analysts to have potential sales of $3 billion to $4 billion a year.

But sales, which totaled $1.27 billion last year, have not taken off as fast as hoped, and the drug has failed to win significant share from Pfizer Inc.‘s $12 billion blockbuster cholesterol treatment Lipitor following controversy over its safety.

The U.S. Food and Drug Administration last year threw out a petition by consumer group Public Citizen to have it banned.

Latest figures show Crestor has a 7.6 percent share of new prescriptions in the U.S. market, up from 6.9 percent in early February.