A large and long-running study shows women who had mammography screening for breast cancer had a greater chance of surviving than those who did not.

The Swedish trial followed more than133,000 women, with researchers dividing them into two groups -- those who received an invitation to a mammography screening, and those who received usual care.

After three decades of study, the researchers found that among the women who were invited to a screening, there were 30 per cent fewer breast cancer deaths.

"Mammographic screening confers a substantial relative and absolute reduction in breast cancer mortality risk in the long-term," said Stephen W. Duffy, professor of cancer screening at Queen Mary, University of London, and an author of the study.

"For every 1,000 to 1,500 mammograms, one breast cancer death is prevented."

The results of the study were published Tuesday in the journal Radiology.

It's the first breast cancer screening trial to show a reduction in mortality as the result of mammography alone.

In total 133,065 women were included in the randomized study. The women in the screening group who were between the ages of 40 and 49 were screened on average every 24 months, over a seven-year period. Those between 50 and 74 were screened about every 33 months, also for seven years.

The study also found that the longer a patient was involved in follow-up screening, the greater their chances of survival.

"Most of the deaths prevented would have occurred more than 10 years after the screening started," Duffy said.

"This indicates that the long-term benefits of screening in terms of deaths prevented are more than double those often quoted for short-term follow-up."

Duffy said the research strongly suggests that if a patient is diagnosed at an early age, and takes part in a recommended screening schedule, their chances of survival are "very good."

Breast cancer survivor Janice Dawes said that such screenings are important because they help potential victims deal with the disease before it becomes critical.

"When I got diagnosed, I could say, ‘wow this is something that I was really fortunate about, because I did catch it early.'"

Dr. Rene Shumak, who works with the Ontario Breast Screening Program, said that the study puts hard numbers to what many in the medical community have advocated for years.

"It's good news because it tells us that breast cancer screening with mammography does work; it decrease mortality from breast cancer."

Still, Dr. Gilbert Welch, of the Dartmouth Institute for Health Policy, said that there is a potential downside with increased testing.

"They lead to a lot of false alarms, and then less commonly -- but it happens -- it leads some people to be diagnosed and treated for breast cancer unnecessarily."

With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip