Mammograms save lives, period, end of story. But it takes decades to appreciate just how many.
That's the takeaway from the longest-running mammogram study -- which followed more than 100,000 swedish women for 29 years -- that many doctors believe will put the recent ruckus over the frequency of breast cancer screening to bed.
The researchers found that seven years of mammograms made for 30 percent fewer breast cancer deaths years down the road, when compared with women who didn't receive mammograms.
"I think this study indicates the absolute benefit of screening in terms of breast cancer deaths prevented," says Stephen Duffy, a professor of cancer screening at Queen Mary, University of London, and lead author of the study.
While the American Cancer Society had long recommended that women over the age of 40 receive yearly mammograms, the U.S. Preventive Services Task Force challenged this recommendation in 2009, calling into question whether the number of lives saved were worth the cost of such regular mammograms and the increased possibility of false positives. In light of the possible adverse effects of yearly screening, the Task Force recommended that women get screened every other year starting at age 50, and stop mammogram screening altogether after age 75.
But the Swedish study, published Tuesday in the Journal Radiology, suggests that when women are followed over the course of decades (in this case 29 years) instead of the seven or so years that many past studies have looked at, mammograms may save many more lives. Among the 133,065 women studied, one breast cancer death was prevented for every 414 to 519 women screened.
"The longer follow-up period, three decades, is crucial. It is important to have this length of time to allow the benefits of screening to become apparent," says Dr. Laurie Margolies, chief of breast imaging at Mount Sinai Medical Center in New York, who was not involved in the Swedish study.
This long-term view is important, in part because certain types of breast cancer can take decades to become lethal, says Dr. Richard Ellis, co-director of the Norma J. Vinger Center for Breast Care in Wisconsin.
"A less aggressive, slow-growing cancer could take 15 to 25 years before it spread to a vital organ, resulting in a breast cancer death," he says. "Thus, a shorter-term follow-up study will likely account only for breast cancer deaths due to the more aggressive cancers. … That is why studies with shorter follow-up … understate the true value of screening mammography."
The Swedish Study and Mammogram Debate
The recent study looked at more than 100,000 women in two counties in Sweden. Beginning in 1977, researchers randomly assigned half the women to receive seven years of regular medical care that did not include mammograms, and the other half to receive regular mammograms -- every two years for those age 40 to 49 and every three years for those age 50 to 74.
When the seven-year trial ended, the researchers followed up with the women for 22 more years. After seven years, all the women were offered mammograms, but only those cancers detected during those first seven years were included in the study's results.
The researchers found that the preventive effect of mammograms became more apparent as the years went by: 10 years after the study began, 71 lives had been saved because of the screenings; 29 years later, 158 lives had been saved, study leader Duffy says.