False positive screening results contribute to more than one million
prostate biopsies a year, the authors note. Down the line,
procedures done as a result of these inaccurate results can lead to
incontinence, erectile dysfunction, hospital admission and deaths.
Mammograms, too, may be problematic, they write, citing Swiss data
showing that these tests avert just one breast cancer death for
every 1,000 women screened.
“There used to be ads saying if a woman hadn’t had a mammogram, she
needed more than her breasts examined,” Prasad said. “The fact that
the medical profession promoted screening so strongly, when it was
always a balancing act, when it was always a personal choice, is
really shameful.”
The strongest evidence that testing for cancer may save lives comes
from a lung cancer study involving more than 53,000 heavy smokers.
Half of the participants got standard chest X-rays and the other
half received more sensitive CT scans. The CT group showed a 20
percent reduction in the risk of lung cancer deaths and a 6.7
percent decline in overall mortality compared to the X-ray group.
But the absolute reduction in deaths from any cause among those
screened was less than half a percent and may have been due to
chance, the authors conclude.
To know if cancer screening truly saves lives, statistically robust
studies based on millions of people are needed, they write,
conceding that it would be expensive, but no more so than supporting
mass population screening programs with unproven benefits.
And without conclusive evidence that screening saves lives, doctors
have an obligation to clearly outline all the potential risks and
benefits of screening to patients so they can make an informed
decision about whether it makes sense in their particular situation,
Dr. Gerd Gigerenzer, director of the Max Planck Institute for Human
Development in Berlin, writes in an accompanying editorial.
Some patients who have the facts and weigh the pros and cons of
screening may indeed benefit, but that doesn’t mean doctors should
overstate the value of tests and encourage patients to go this route
all of the time, Gigerenzer writes.
“The take-home message is after decades of research we have not
found clear evidence that screening saves lives, but clear evidence
that screening harms many,” Gigerenzer added by email.