Regular screening mammography can reduce breast cancer deaths by up to 44%, according to a large Swedish study published in the latest issue of Cancer (July 22, 2002, Vol. 95:3, pp. 451-457).
The study offers a much-needed boost to mammography advocates, who have faced intense debate on the efficacy of screening mammography ever since the publication of a Danish study two years ago that questioned mammography's value in saving lives (The Lancet, January 8, 2000 Vol. 355:9198, pp. 129-134).
In the new study, Dr. Lars Holmberg and colleagues from Uppsala University in Sweden studied breast cancer data in seven counties that represent 33% of Sweden's women. The counties had all implemented extensive mammography screening programs between 1978 and 1989, in which women were screened every 1 1/2 to two years.
The researchers used centralized health data to compare breast cancer mortality statistics in the years before the screening program began with the same statistics in the years following implementation of the program. In addition to geographic matching of subjects by county, the investigators used prescreening and post-screening epochs of the same duration to avoid bias due to a death hazard that varies with the amount of time since diagnosis.
The programs screened women in 6 counties between the ages of 40 and 69, and in one county between the ages of 50 and 69.
According to the study results, there were 5,278 incidences of breast carcinoma before screening began, and 8,364 incidences detected during the screening epoch. The number of breast cancer deaths were 1,169 and 875, respectively.
Between the prescreening and screening epochs, death from breast cancer was reduced by 44% (relative risk = 0.56, with a 95% confidence interval) among women who were actually screened.
When all tumors were considered, i.e., when those exposed and those unexposed to screening were combined, counties that had been screening for more than 10 years saw breast cancer mortality reduced by 32%. In contrast, counties that had screening programs in place for 10 years or less had an 18% reduction in breast cancer deaths, the study authors wrote.
"The policy of offering screening is associated with a mortality reduction in breast carcinoma of 30% in the invited population, exposed and unexposed combined," they stated. "The results of the current study indicate that the majority of the breast carcinoma mortality reduction is indeed due to the screening."
In an editorial accompanying the Cancer article, Dr. Stephen Feig of Mount Sinai Hospital in New York City noted that the Swedish trial results are similar to trends in the U.S., where breast cancer mortality has decreased by approximately 39% since 1980 for the average patient with invasive breast cancer.
"The proportions of this estimated gain attributable to greater breast health awareness, increased utilization of screening mammography, and better treatment cannot be precisely determined," Feig wrote. "However, further gains may be anticipated as more women comply with American Cancer Society screening guidelines."
By Eric Barnes
AuntMinnie.com staff writer
August 1, 2002
Lancet study reiterates benefits of breast cancer screening, March 15, 2002
U.S. panel affirms support for mammography, February 22, 2002
Panel casts more doubt on mammography's value, January 24, 2002
Reassessment confirms: Screening mammography has no survival benefit, October 19, 2002
Danish mammo study reviewed: right questions, wrong answers, January 17, 2000
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