Mammograms Leading to Treatment of Breast Cancers
that May Have Disappeared Later
Study find women screened most often have the most
cancer detections, regardless of age
Nov. 24, 2008 Some breast cancers just disappear.
At least that is the conclusion used to explain recent discoveries that
women screened by mammography every six years had lower rates of breast
cancer than those screened every two years. Some of the cancers detected
by mammography may have spontaneously regressed had they not been
discovered and treated in the Norwegian women.
When the screening of women in four counties began
every two years, the breast cancer rates increased significantly,
according to the report in the November 24 issue of Archives of Internal
Medicine, one of the JAMA/Archives journals.
Throughout Europe, the start of screening
mammography programs has been associated with increased incidence of
breast cancer, according to background information in the article.
"If all of these newly detected cancers were
destined to progress and become clinically evident as women age, a fall
in incidence among older women should soon follow," the authors write.
"The fact that this decrease is not evident raises
the question: What is the natural history of these additional
screen-detected cancers?"
Per-Henrik Zahl, M.D., Ph.D., of the Norwegian
Institute of Public Health, Oslo, and colleagues examined breast cancer
rates among 119,472 women age 50 to 64 who were all invited to
participate in three rounds of screening mammograms between 1996 and
2001 as part of the Norwegian Breast Cancer Screening Program.
They compared these to rates among a control group
of 109,784 women age 50 to 64 in 1992, who would have been invited for
screening if the program had existed at that time.
Cancers were tracked for six years using a national
registry, and at the end of that time all participants were invited to
undergo a one-time screening to assess breast cancer prevalence.
As anticipated, breast cancer rates were higher
among screened women than among the control group before the final
prevalence screening.
"Even after prevalence screening in controls,
however, the cumulative incidence of invasive breast cancer remained 22
percent higher in the screened group," according to the report.
Of every 100,000 screened women, 1,909 had breast
cancer during the six-year period, compared with 1,564 of every 100,000
in the control group.
Screened women were more likely to have breast
cancer at every age.
"Because the cumulative incidence among controls
never reached that of the screened group, it appears that some breast
cancers detected by repeated mammographic screening would not persist to
be detectable by a single mammogram at the end of six years," the
authors write.
"This raises the possibility that the natural
course of some screen-detected invasive breast cancers is to
spontaneously regress."
"Although many clinicians may be skeptical of the
idea, the excess incidence associated with repeated mammography demands
that spontaneous regression be considered carefully," they continue.
"Spontaneous regression of invasive breast cancer
has been reported, with a recent literature review identifying 32
reported cases.
This is a relatively small number given such a
common disease. However, as some observers have pointed out, the fact
that documented observations are rare does not mean that regression
rarely occurs. It may instead reflect the fact that these cancers are
rarely allowed to follow their natural course."
The findings do not answer the question of whether
mammograms prevent deaths from breast cancer, the authors note.
"Instead, our findings simply provide new insight on what is arguably
the major harm associated with mammographic screening, namely, the
detection and treatment of cancers that would otherwise regress," they
conclude.
Editorial: Results emphasize our lack of
knowledge regarding cancers natural history
"Despite the appeal of early detection of breast
cancer, uncertainty about the value of mammography continues," write
Robert M. Kaplan, Ph.D., of the University of California, Los Angeles,
and Franz Porzsolt, M.D., Ph.D., of Clincal Economics University of Ulm,
Germany, in an accompanying editorial. "In this issue of the Archives,
Zahl et al use a clever study design in an attempt to estimate the value
of screening."
"Perhaps the most important concern raised by the
study by Zahl et al is that it highlights how surprisingly little we
know about what happens to untreated patients with breast cancer," Drs.
Kaplan and Porzsolt continue. "In addition to not knowing the natural
history of breast cancer for younger women, we also know very little
about the natural history for older women. We know from autopsy studies
that a significant number of women die without knowing that they had
breast cancer (including ductal carcinoma in situ). The observation of a
historical trend toward improved survival does not necessarily support
the benefit of treatment."
"If the spontaneous remission hypothesis is
credible, it should cause a major re-evaluation in the approach to
breast cancer research and treatment. Certainly it is worthy of further
evaluation," they conclude.
Editor's Note: This study was supported in
part by a Research Enhancement Award from the Department of Veterans
Affairs.
Links to More
News Reports About Breast Cancer and Older Women
Nov. 24, 2008 Some breast cancers just disappear.
At least that is the conclusion used to explain recent discoveries that
women screened by mammography every six years had lower rates of breast
cancer than those screened every two years. Some of the cancers detected
by mammography may have spontaneously regressed had they not been
discovered and treated in the Norwegian women.