US Study: Breast cancer screening does not save lives
BMJ 2005;331:309 (6 August)
Breast cancer screening does not save lives, study says Janice Hopkins Tanne
Breast cancer screening in "real world" situations is not effective in preventing mortality, says a US case control study. The study, one of the largest completed to date looking at the effectiveness of breast cancer screening, was published in the Journal of the National Cancer Institute ( 2005;97: 1035-43) [Abstract/Free Full Text].
Randomised controlled studies have shown that breast cancer screening prevents deaths. Many organisations recommend screening by clinical examination and mammography every year or two for women aged 40 or older.
"We observed no appreciable association between breast cancer mortality and screening history, [regardless of age or risk level]," the authors write. "Our findings may, therefore, reflect a possible reduction in the accuracy of screening as it moves from highly controlled randomised trials to real-life clinical practice."
The study, led by Joann Elmore, professor of medicine at the University of Washington School of Medicine, Seattle, looked at the history of screening in the three years before their diagnosis of cancer in 1351 women who died of breast cancer between 1983 and 1998. They compared these screening rates with those in a control group of 2501 cancer-free women, matched for age (40-49 years or 50-65 years) and risk of developing cancer (average risk or greater risk because of family history or a breast biopsy).
The authors thought that if screening prevents women from dying from breast cancer then the number of women who had been screened would be higher in the cancer-free group. However, screening rates in the two groups did not differ.
Among women aged 40 to 49 and in the average risk group, 66% of women who had cancer and 64% of women in the control group had been screened. Among women in the same age group but at greater risk, 78% of women who had cancer and 81% of controls had been screened. Among women aged 50 to 65, in the average risk group 70% of women who had cancer and 69% of the controls had been screened, and in the high risk group 81% of women who had cancer and 85% of controls had been screened. None of these differences was significant.
In all the women in the high risk group (in both age groups), breast cancer mortality was a non-significant 26% lower among women who had been screened than among those who hadn't undergone screening. The odds ratio for an association between breast cancer mortality and screening was 0.74 (95% confidence interval 0.53 to 1.03) in the high risk group and 0.96 (0.80 to 1.14) in the average risk group. The difference was not statistically significant (P=0.17).
The women were enrolled in six well regarded health plans in Seattle, Boston, Minneapolis, Portland (Oregon), northern California, and southern California that offered breast cancer screening. About 30% of the women were not white.
The screening was by clinical examination alone, mammography alone, or clinical examination and mammography. Mortality did not differ according to type of screening.
Despite the study's findings, Dr Elmore said that she still recommended screening. "Some people say we should pay more attention to women at high risk, but the majority of women who develop breast cancer don't have risk factors," she said.
In an accompanying editorial Russell Harris of the University of North Carolina, Chapel Hill, said that breast cancer screening in the community may be less effective than in controlled trial situations because of problems implementing programmes.
Women are now more aware of the importance of checking out small lumps, and better treatment may mean that screening is less necessary than previously, because treatment of later stage cancers may still be effective.