May 2 (HealthDay News) -- Prompt treatment of a common stomach infection reverses the damage that can lead to gastric cancer, according to tests on mice done by researchers at the Massachusetts Institute of Technology (MIT).

The findings should put a stop to any questions about whether, and when, antibiotic treatment of Helicobacter pylori can reduce or eliminate the risk of developing stomach cancer.

"We concluded that H. pylori eradication prevented gastric cancer to the greatest extent when antibiotics were given at an early point of infection, but that eradication therapy given at a later point also delayed the development of severe lesions that can lead to cancer," study author James G. Fox, director of the division of comparative medicine at MIT, said in a prepared statement.

Stomach cancer is the second-leading cause of cancer death worldwide and about half the world's population is infected with H. pylori, which is recognized as a major cause of both peptic ulcers and stomach cancer. It typically takes several decades for stomach cancer to develop in people who are susceptible -- about 3 percent of people infected with H. pylori.

It's been unclear when doctors should screen and treat people with antibiotics -- other than immediate relatives of patients with stomach cancer and peptic ulcer disease -- or when to treat H. pylori infection for maximum benefit, Fox said.

He and his colleagues created mice prone to accelerated H. pylori infection and progression to stomach cancer. The researchers found that mice treated with antibiotics had less severe disease at every stage of advancing infection.

Mice treated eight weeks post-infection had the same risk of cancer as uninfected mice. However, treatment at 12 and 22 weeks post-infection didn't reverse damaging changes, such as inflammation and development of precancerous lesions, to levels seen in uninfected mice.

"Our mouse model mimics the progressive process we know occurs in the development of human gastric cancer. This [study] shows early intervention provides the maximum benefit," Fox said.

The study appears in the May 1 issue of Cancer Research.

American Association for Cancer Research, news release, May 1, 2008