NCI study affirms that breast screening saves lives

Validation of screening mammography as a life-saving tool comes as no surprise to breast imagers, who have known all along that early detection of breast cancer is a key component to reducing mortality. Now they hope the focus will turn toward encouraging women to obtain annual screening mammography exams.

In a study published Thursday in The New England Journal of Medicine, statisticians appointed by the National Cancer Institute evaluated the relative contributions of screening mammography and adjuvant treatment to decreased breast cancer mortality between 1975 and 2000 (NEJM 2005;353:1784-1792). Breast cancer deaths dropped by 21.3% during the study period. Screening mammography is responsible for nearly half of that reduction, researchers found.

"I'm happy to see data that support the efficacy of mammography to reduce breast cancer mortality," said Dr. David Dershaw, chief of breast imaging at Memorial Sloan-Kettering Cancer Center in New York City, in an e-mail to Diagnostic Imaging. "But debates about the percentage contribution are not particularly valuable."

Clinical trials in Sweden and the Netherlands have already affirmed mammography's value as an early cancer detection tool, said Dr. Daniel Kopans, chief of breast imaging at Massachusetts General Hospital, in an e-mail to Diagnostic Imaging. He considers such trials a more direct way of measuring mammography's benefit than the computer modeling conducted by the NCI team.

"The NEJM study is one more analysis that confirms the remarkable benefit of mammography screening in decreasing mortality when introduced into the general population," he said. "Most of the existing data point to mammography contributing most of the benefit, with 15% to 20% of the decrease in mortality coming from improved therapy."

It is also clear that the biggest benefits are seen among women who begin screening by age 40, he said.

Dershaw, who penned an editorial accompanying the study in the NEJM, also noted that much of the increased cure rate of breast cancer is due to early detection. While mammography plays an important role in breast cancer mortality, it's not a solo player.

"Early detection does not work in a vacuum," he said.

Some smaller cancers now curable by chemotherapy or hormone therapy would be fatal if found at a later stage, Dershaw said. Other cancers can now be cured by surgery when detected before they have spread.

"The battle against breast cancer has been fought with many weapons: early detection with mammography, better drugs, better surgery, and better radiation," he said. "The combination of these efforts offers more hope to women with breast cancer that they can be cured. But the increased opportunity for cure often hinges on early detection of cancer by mammography."

The NCI embarked on the study in part to resolve controversies regarding mammography's contribution to reduced mortality and to understand why breast cancer deaths fell so rapidly between 1990 and 2000.

While the breast cancer mortality rate was nearly flat between 1975 and 1990, rates dropped dramatically thereafter, from 49.7 per 100,000 women in 1990 to 38 per 100,000 women in 2000, according to the study.

The seven research teams engaged by the NCI developed statistical models of breast cancer incidence and mortality and then applied those models to the same data set. Each group used the same sources to obtain data on the use of screening mammography, adjuvant treatment, and the benefits of treatment with respect to death rates from cancer.

Actual benefit from screening mammography ranged from 28% to 65% among the seven groups, with a median of 46%.

"The controversies of the past need to be laid to rest, so we can concentrate on continuing to decrease the number of deaths from breast cancer," Kopans said. "Women need to be encouraged to participate in screening on an annual basis beginning by age 40."