The study, which involved 7,301 patients, found that 71 percent of confirmed breast cancer deaths occurred in the 20 percent of the study population that did not receive regular mammograms. The majority of those who died from breast cancer never had a mammogram prior to diagnosis. If treatment were the primary survival factor, deaths would not have been so prevalent among the non-screened group.

Moreover, 50 percent of the breast cancer deaths occurred in women under the age of 50, while only 13 percent were in women ages 70 or older. For women who died of breast cancer, the median age at diagnosis was 49; for those dying of any other cause, the median age at diagnosis was 72. This suggests that women under 50 are a primary group in which greater screening compliance would provide the greatest benefit.

"These findings should quiet those who argue that women age 40-49 do not need regular mammography screening. In fact, these women need annual screening -- as do all women 40 and older. This is the message physicians should be promoting," said Barbara S. Monsees, MD, FACR, chair of the American College of Radiology Breast Imaging Commission. "Breast cancer treatment has come a long way, but, as this study demonstrates, these advances have not negated the value of, or the need for early detection. This is especially true for younger women, who tend to have faster growing tumors."

Unlike previous studies on the value of mammography that have shown varying benefits, these findings provide more definitive information through a technique called "failure analysis" -- which looks backwards from death to discover correlations at diagnosis. Harvard Medical School Professor of Surgery (emeritus) Blake Cady, MD, and his colleagues followed cases of invasive breast cancer diagnosed between 1990 and 1999 at Partners HealthCare hospitals through 2007, analyzing demographics, mammography use, surgical and pathology reports and recurrence and death dates to discover correlations.

"This study should effectively end confusion over when, and particularly if, women need to begin screening. Every year, breast cancer takes too many of our mothers, wives, sisters and friends. While these findings cannot bring back those already lost, they clearly demonstrate that mammography saves lives, and many more deaths can be avoided through regular screening," said Murray Rebner, MD, FACR, president of the Society of Breast Imaging.

While breast cancer mortality has been on steady decline (about 2 percent per year) in the last two decades, the majority of deaths that are still occurring are in women who do not receive regular mammograms. With more prevalent screening, especially in younger women, the study suggests that breast cancer mortality could decrease to much less than 10 percent overall in the next ten years, and perhaps to as low as 5 percent overall by 2030.