NEW YORK, Jan 07 (Reuters Health) -- A report published this week in The
Lancet questions whether screening for breast cancer using mammography saves
lives.
From their re-examination of the way six studies of mammography screening
were conducted, Danish researchers conclude that "there is no reliable evidence
that screening decreases breast cancer mortality."
But an expert with the American Cancer Society counters this conclusion,
noting that the results of individual studies show that detection of breast
cancer using mammography does in fact save lives.
Because a 1999 Swedish study showed no decrease in breast cancer deaths
even though mammography screening has been recommended there since 1985, Drs.
Peter C. Gotzsche and Ole Olsen of the Nordic Cochrane Centre in Copenhagen,
Denmark, evaluated eight published mammography screening studies. These trials
included a half million women and had taken place in the United States, Canada,
Scotland, and Sweden.
In six of the trials, Gotzsche and Olsen determined that the randomization
process -- part of the study method, where women were randomly assigned to
having screening or not having screening -- had not created similar groups in
terms of characteristics such as age and socioeconomic status. This may have
introduced bias, that is, affected the study results, they report. In four of
the trials, the number of women randomized was inconsistent.
In the two trials where the investigators determined that randomization
was adequate, the study results suggests that mammography screening had no
effect on the risk of death from breast cancer or death from other causes. In
the other six trials where the researchers had identified bias, meaning that the
design of the study may have affected the results, the risk of dying from breast
cancer was 25% lower than in the unbiased trials.
A previous analysis of five Swedish trials had shown a decrease in deaths
from breast cancer but an increase in total deaths, although the increase in
total deaths disappeared after adjusting for age.
Based on their analysis, Gotzsche and Olsen conclude, "Screening for
breast cancer with mammography is unjustified."
But in an accompanying editorial, Dr. Harry J. de Koning of Erasmus
University Rotterdam in the Netherlands, who is also a member of the National
Evaluation Team for breast cancer screening in the Netherlands, questions the
researchers' reasoning, and their conclusion that certain mammography screening
trials were not adequately randomized.
Although de Koning acknowledges that nine years of screening in the
Netherlands has not significantly reduced deaths from breast cancer in that
country, he notes that the number of deaths from breast cancer have fallen in
the UK, in part due to screening, and a screening program in Finland seems
likely to do the same.
"Publication of the reports, whether the results are positive or negative,
together with the seeking of the opinions of women, are the ways by which an
answer can be reached as to whether or not screening programmes are justified
and at what cost to women and to society," de Koning writes.
In an interview with Reuters Health, Dr. Robert Smith, director of cancer
screening at the American Cancer Society, noted that his organization and other
organizations have evaluated the results of screening trials many times over the
past 30 years.
"We and others have scrutinized the randomization process in all of these
studies as well, and have not found any basis for questioning the fundamental
conclusions that have been drawn from the individual studies in the
meta-analysis, and that is that mammography saves lives from breast cancer," he
said.
