New Study Validates Benefits of Mammograms
Regular mammograms reduce breast cancer deaths by up to 44%, according to a major new study that involved a third of the women in Sweden.
The efficacy of mammography has been the subject of great debate over the last year or so, based in large part on a Danish study claiming that clinical trials of breast screening had procedural and other flaws that rendered them meaningless.
Most major health organizations have since reaffirmed their belief in the value of screening, but doubts raised by critics have left many women concerned about the need for mammograms and their potential benefits. The new study may finally lay some of those doubts to rest.
The results, published today in the journal Cancer, “effectively refute” the claims that mammography is not beneficial and “confirm beyond any doubt” that reductions in deaths can be obtained in large screening programs, said Dr. Stephen A. Feig of Mount Sinai Hospital in New York City.
“This is a very impressive study that is going to change a lot of people’s minds about mammography,” added Dr. Larry Norton of the Memorial Sloan-Kettering Cancer Center in New York, president of the American Society for Clinical Oncology. “It seems very compelling that the benefits might be even more than we had anticipated.”
The new study is by far the largest ever to examine the potential benefits of mammography. Its design apparently eliminates the flaws that led critics to reject some earlier studies.
“I would hope that it would cause some people who have been very critical of mammography to look at it very carefully and to find that many of the limitations they focused on” are not present here, said Robert A. Smith of the American Cancer Society, an epidemiologist who participated in the study.
“The debate had grown bigger than the data. Now we can move on to researching how to do the best job we can at finding breast cancers when they are very small and treatable.”
An estimated 190,000 American women are diagnosed with breast cancer each year, and more than 40,000 will die of it. Current U.S. guidelines issued by the American Cancer Society, the American Medical Assn. and other groups recommend that women over age 40 have an annual mammogram.
Critics note, however, that only 20 out of every 100 positive mammograms actually indicate the presence of a cancer. The false positives, they charge, expose women to many serious diagnostic procedures, such as breast biopsies, without any proof of benefit. The new study would seem to provide that proof.
An international team of researchers headed by Dr. Lars Holmberg of Uppsala University studied breast cancer in seven Swedish counties that include roughly 33% of the country’s women. The counties each began extensive mammography programs between 1978 and 1989, screening women every 1 1/2 to two years.
Using the centralized health data available in Sweden, the team examined cancer deaths in each county in the years immediately before widespread screening began and then in the period afterward. Six of the counties screened women beginning at age 40, and one at age 50.
Among the women who were actually screened, the death rate from breast cancer was reduced by 44%, compared with rates in the pre-screening period.
Some proponents of screening have argued that earlier studies, which showed no benefit from mammography, did not have a long enough follow-up period. The new results support that contention. In the counties in which screening had been offered for 10 years or less, the overall reduction in deaths was 18%, while in those that had offered it for more than 10 years, the reduction was far higher.
“I think this clinches the case for mammography,” Norton said.
“This is just about the best way you can do such a study,” said Dr. Lawrence Bassett, director of the Iris Cantor Center for Breast Imaging at UCLA’s Jonsson Comprehensive Cancer Center. “But I am not surprised by the results because they are in line with what we have been finding in our own patients.”
That seems to be the experience elsewhere as well. In an editorial in the same issue of Cancer, Feig noted that there has been a 39% reduction in deaths for the average patient with invasive breast cancer since 1980. Some of that is clearly due to better treatments, but much of it is also due to earlier detection, he said.
