Updated from 12:14 p.m. ESTA two-year study shows that AstraZeneca's ( AZN) cholesterol fighter Crestor reversed plaque buildup in the arteries of patients with evidence of coronary artery disease. AstraZeneca says the results mean that for the first time, a drug from the class known as statins has shown an ability to reverse atherosclerosis in a major clinical study. Atherosclerosis occurs when deposits of fatty substances, cholesterol or cellular waste products collect in the inner lining of an artery, forming a buildup called plaque. If plaque ruptures, it can block the flow of blood to organs such as the heart or the brain and can lead to a heart attack or stroke. Data from a trial called Asteroid were presented at the American College of Cardiology meeting in Atlanta. According to the study, the plaque content in patients' arteries was reduced by 7% to 9%. Crestor also contributed to a 53% reduction in LDL, or "bad" cholesterol and a 15% increase in HDL cholesterol, the "good" kind. Pfizer ( PFE), whose Lipitor is not only the top-selling statin, but the biggest-selling drug in the world, took exception to some of AstraZeneca's statements. "Only Lipitor has demonstrated significant LDL reductions and cardiovascular benefits for a wide range of patients, with an excellent efficacy and safety profile across the full dose range," the company said in a press release responding to the Crestor data. "This is not the first time a statin has demonstrated plaque regression." Pfizer said in a trial that compared Lipitor with another lipid-lowering agent over 18 months, a 5.9% total plaque reduction was seen in a subset of patients. Companies selling cholesterol-reducing drugs are battling for position in what is a huge market. Crestor's sales totaled $1.27 billion last year. By comparison, Pfizer sold more than $12 billion of Lipitor in 2005.