The longest study yet to examine women who undergo mammography shows that it reduces death from breast cancer by at least 30 percent, a finding that many doctors say may help ease the recent controversy surrounding the procedure.
The three-decade study in Sweden showed that a breast cancer death is prevented for every 414 to 519 women who are screened, a much lower number than the 1,000 to 1,500 that had been projected in previous studies.
"What this tells us is that, in the long term, screening for breast cancer is a very good investment," said epidemiologist Robert A. Smith, director of cancer screening at the American Cancer Society and a co-author of the paper appearing in the journal Radiology.
Critics had argued that overuse of the procedure produced too many false positives, requiring many women to undergo unnecessary invasive procedures.
"There is little question that there is some overdiagnosis," Smith said, "but the number we have identified is really quite small. We estimated it is less than half the number of lives saved, so it is really pretty low."
The findings are "a really big deal," said Dr. Loretta Lawrence, chief of breast imaging at North Shore University Hospital in Manhasset, N.Y. "A 30 percent reduction in mortality translates to 15,000 to 20,000 lives saved by mammography screening each year."
The new study does not address the controversy surrounding the value of screening women in their 40s because the results did not stratify women by age. Nor does it address the controversial issue of how frequently a woman should have a mammogram.
In the United States, mammograms are generally recommended annually, and some scientists have argued that the period between screens should be lengthened. The women in the study were screened less frequently: every 24 months for women ages 40-49, and every 33 months if older than that.
The new findings are unlikely to change clinical practice in the United States because professional groups already recommend routine screening.
But Dr. H. Gilbert Welch of the Dartmouth Institute for Health Policy and Clinical Practice, who has argued that women are being overscreened, said the studies don't take into account advances in breast cancer therapy. As the treatments have improved, the vast majority of patients have done well, regardless of how early their tumors were diagnosed.
Nobody's arguing that mammography doesn't save lives, said Dr. Susan Love, head of the Dr. Susan Love Research Foundation in Santa Monica, Calif. "Really, what has been the source of more controversy is: What is the right schedule? This doesn't really add to that discussion."