Breast cancer: myths and facts
Overtreatment of cancers
Breast cancer is the
leading type of cancer and cause of cancer deaths in women worldwide. Nearly
1.4 million new cases are diagnosed each year. Many studies have found that
mammography saves lives, but how many and for what age groups is debatable. It
also causes many false alarms and overtreatment of cancers never destined to
In the US, a
government-appointed task force that gives screening advice does not back
mammograms until age 50, and then only every other year. The American Cancer Society
recommends them every year starting at age 40.
Other countries screen less
aggressively. In Britain, for example, mammograms are usually offered only
every three years.
Canadian study pessimistic
The Canadian study has long
been the most pessimistic on the value of mammograms. It initially reported
that after five years of screening, 666 cancers were found among women given
mammograms plus breast exams versus 524 cancers among those given the exams
After 25 years of
follow-up, about 500 in each group died, suggesting mammograms were not saving
lives. The similarity in the death rates suggests that the 142
"extra" cancers caught by mammograms represent over diagnosis – tumours
not destined to prove fatal, study leaders concluded.
The work was immediately
criticised. The American College of Radiology and Society of Breast Imaging
called it "an incredibly misleading analysis based on the deeply flawed
and widely discredited" study. Mammograms typically find far more cancers
than this study did, suggesting the quality was poor, the groups contend.
Experts speak out
In a letter posted by the
medical journal, Dr Daniel Kopans, a radiologist at Harvard Medical School,
described outdated machines and methods he saw in 1990, when he was one of the
experts asked to review the quality of mammograms used in the study.
"I can personally
attest to the fact that the quality was poor," he wrote. "To save
money they used second-hand mammography machines" that gave poor images,
failed to properly position breasts for imaging, and did not train radiologists
on how to interpret the scans, he wrote.
Read: Preventing breast cancer
The study leader, Dr
Anthony Miller of the University of Toronto, said it was "completely
untrue" that inferior equipment or methods were used.
Still, the study highlights
the fact that mammograms are an imperfect tool that lead to many false alarms,
needless biopsies and treatment of many tumours that would never threaten a
"Over diagnosis is not
an anomaly in the study from Canada. This has been compellingly demonstrated in
research from the US and Europe," said another study leader, Dr. Cornelia
Baines of the University of Toronto.
Dramatic improvement in treatments
Dr H. Gilbert Welch, a
professor of medicine at the Dartmouth Institute for Health Policy and Clinical
Practice in New Hampshire, spoke on the issue at the San Antonio Breast Cancer
Symposium in December.
"Screening is a
choice, not a public health imperative. There are trade-offs here," he
"The people who stand
to gain the most from screening are the people at greatest risk of the
disease" – older women who are more likely to have breast cancer and those
not too old that they are likely to die of something else, he said.
Read: How is breast cancer treated?
Death rates from breast
cancer have fallen mostly because of dramatic improvement in treatments, he and
other doctors have said.
"The better we are at
treating clinically evident disease, the less important it becomes to find it
early," Welch said.
A big caveat: The Canadian
study was on routine mammograms to screen healthy women. No one doubts the
value of diagnostic mammograms – more detailed X-rays when a problem is
suspected or after a lump has been found.
Picture: Mammogram from Shutterstock
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