Mammography works. That’s the conclusion of a study and an editorial reported in the August 1 issue of the journal Cancer (Vol. 95, No. 3: 458-69, 451-57).

The study was conducted by Stephen W. Duffy, MSc, from Cancer Research UK in London, United Kingdom, and 22 other experts from around the world. They looked at deaths from breast cancer in seven counties in Sweden, both before and after community mammography programs began.

Recently, there have been conflicting reports about the value of mammography, and whether it decreases deaths from breast cancer.

In this study, the authors pointed out that it is important to look at two groups — breast cancer deaths from breast cancer diagnosed before mammography programs were started and deaths from breast cancer diagnosed after mammography programs were in place for a number of years, preferably 10 years or more.

That’s the time it takes to start to see the benefits of mammography, according to the authors. Mammography may be available in a community, but it may take several years until all the women who want mammograms actually have one.

And, for those women who don’t want a mammogram, there appears to be a higher rate of death from breast cancer, according to the report. The reasons for this are unclear.

Without considering these factors, it is impossible to tell how effective mammography is in reducing the risk of death from breast cancer, noted the authors.

Not every county had the same age groups screened at the same time between screenings. For example, in one county, Dalarna, women aged 40 to 69 were screened every 18 to 33 months. In Varmland, women ages 50 to 69 were screened every 18 months.

The American Cancer Society (ACS) screening recommendations vary slightly from those used in Sweden.

By carefully examining information from the seven Swedish counties before and after community screening programs were started, the study found a large decrease in the number of women dying from breast cancer after screening had been in place for several years.

For the seven counties together, breast cancer deaths decreased 45% in women who actually had a screening mammogram. In one county, where screening had been in place for over 10 years (Dalarna county), deaths from breast cancer decreased 60% compared to death rates before screening.

The authors pointed out that not all of the decrease in breast cancer deaths is due to screening alone.

Before mammography was available in these counties, the death rates from breast cancer had been falling by about 1% per year, according to the authors.

"This can be considered to be the combined effect of increased public awareness resulting in more rapid reporting of breast symptoms, changes in the availability of diagnostic and treatment facilities, improvements in therapy, and patient management," they said.

But, they said, at the same time, the incidence of breast cancer was increasing in these counties. That means that the majority of the benefit in decreasing breast cancer deaths is related to mammography, the authors reported.

"The results of the current study, which evaluated the results of service screening in 33% of the population of Sweden, demonstrate that the results from the randomized trials are reproducible when large-volume, well-organized screening programs are performed in dedicated mammography screening centers," the authors said.

Robert Smith, PhD, one of the study authors and director of screening for the ACS, emphasized the importance of this study.

"This study represents an important new direction for breast cancer screening," said Smith. "There is not likely going to be another trial for mammography. This study measures how screening is performing in the community. We can measure the benefit in women who actually got tested.

"These data show that well-organized screening programs can achieve high quality and contribute to a reduction in breast cancer deaths," said Smith.

But, as Smith noted, Sweden is not the US. Their health care system is better organized to help women get mammograms, and to follow them over time. And, he said, more women get screened in Sweden than in the US.

"Will we find a way in the United States to organize screening to match these results or do better?" asked Smith. "We are not screening systematically. This means we are not achieving the level of benefit from mammography as demonstrated by this report," he said.

An editorial in the same journal, by Stephen Feig, MD, from Mount Sinai Hospital in New York, said that prior clinical trials may have actually understated the benefits of mammography.

In addition, said Feig, there have been improvements in mammography equipment and technique since the earlier trials were performed. This may have led to even further improvements in doctors' ability to diagnose breast cancer on mammograms.

"Advances in mammographic equipment and technique should allow for greater mortality reductions than demonstrated in randomized clinical trials that were conducted in past years," wrote Feig.

The length of follow-up and how often mammography is performed can also influence the benefits and success of mammography in finding breast cancer early, said Feig.

"The results from the study by Duffy [and colleagues], as well as those from seven other reports regarding mammography service screening in Sweden and Finland, confirm beyond any doubt that the substantial reductions in breast carcinoma mortality found in the randomized clinical trials also can be obtained in non-research, organized screening settings," Feig said.

Despite a marked increase in the number of breast cancers in the US from 1980 to 1999, Feig said, there has been a 17% decrease in breast cancer deaths from 1990 to 1999. The expected increased death rate during that time was almost 37%, according to Feig.

"This would suggest that the actual reduction in beast carcinoma mortality between 1990 and 1999 was approximately 39% for the average patient with invasive breast [cancer]," Feig said.