The use of aspirin and other nonsteroidal anti-inflammatory drugs significantly reduces the risk for cancer, but no one has been able to explain why. Now researchers have found that these drugs slow the accumulation of a type of DNA change called somatic genome abnormalities, or S.G.A.’s, that lead to uncontrolled cell growth.

The scientists studied 13 people with Barrett’s esophagus, a condition in which cells in the esophagus become damaged, usually by acid reflux. Sometimes the cells become precancerous, and rarely the problem leads to esophageal cancer.