Two new European studies provide more evidence that mammography can save lives. The studies, from Sweden and the Netherlands, show that death rates from breast cancer declined after screening mammography programs were introduced.

The works are published in The Lancet (Vol. 361, No. 9367: 1405-1410 and 1411-1417).

Among American women, breast cancer is the second most common cancer and the second leading cause of cancer deaths. The American Cancer Society estimates that more than 211,000 US women will get breast cancer this year, and nearly 40,000 will die from it. ACS screening guidelines recommend that women 40 and older get an annual mammogram and clinical breast exam to help detect tumors in the early stage, when they are easier to treat.

In the past few years, though, some researchers have questioned the value of mammograms for preventing deaths from breast cancer, particularly among women in their 40s. The new studies re-enforce the prevailing expert opinion that screening has significant lifesaving value.

In the Swedish study, researchers from Central Hospital in Falun, Sweden, compared the breast cancer death rates in two counties for the 20 years before routine screening was introduced (in 1978) and the 20 years after screening was in place. Data from 210,000 women aged 20-69 were analyzed.

Women aged 40-54 were offered mammograms every 18 months, while women 55 and older were offered screening every two years. Women younger than 40 were not offered mammograms. About 85% of eligible women got screened.

The researchers found that fewer women were dying from breast cancer after mammography became routine, even though more women were getting the disease.

In the period after mammography was introduced, breast cancer deaths dropped 44% among women aged 40-69 who got mammograms, but decreased just 16% among those in that age group who were not screened.

Among women aged 40-49, for whom screening has been controversial, deaths from breast cancer dropped 48% in the group who got mammograms, compared to a 19% decline for those who did not.

The fact that breast cancer deaths were also reduced in women who did not get mammograms may suggest that improvements in treatment and a trend towards faster reporting of breast symptoms to doctors also played some role in reducing mortality. But the larger reductions in the mammography group show that the screening was the more a significant factor, said study co-author Robert Smith, PhD, director of screening for the American Cancer Society.

“Women who got mammograms had much greater mortality reduction than women who did not,” said Smith. “That tells us very clearly that no matter how much progress we’ve made in improving therapy, treatment will most likely be successful if a cancer is diagnosed when it is very small.”

In the Dutch study, researchers from the Erasmus Medical Center in Rotterdam examined the data on nearly 28,000 women (aged 55-74) who died of breast cancer between 1980 and 1999.

They found that death rates from breast cancer had been increasing by 0.3% a year until national mammography screening was introduced in the 1990s. Once screening programs were in place, however, that trend reversed and the death rate from breast cancer began to drop by 1.7% a year. Screening was offered every other year to women aged 50-69.

By 2001, the death rate from breast cancer among women in the study group had dropped 20% compared to 1986-1988, before screening was introduced.

The Dutch researchers also attributed the declines in breast cancer mortality primarily to screening, rather than to improvements in treatment.

Smith said mammography saves lives by detecting tumors earlier than they would otherwise be found.

“Treatments have an opportunity to be most effective when a patient has a very small, early-stage tumor,” he said.

Getting screened yearly, as the American Cancer Society recommends, offers even greater protection than screening at the 18-month or two-year intervals used in the European studies, Smith said.

That’s especially true for women in their 40’s, he said, who tend to develop faster-growing tumors. If screening is done less frequently, the tumors have more opportunity to grow into a cancer that is more difficult to treat.

Editor's note: The American Cancer Society provided financial support for the Swedish study through a gift from the Longaberger company.