Science is an
uncertain science. That’s been brought home once more this past week with all
the consternation over mammography.
“The
Screening Mammography Program Saves Lives,” says the headline on the B.C.
Cancer Agency’s on-line writeup about mammography, a type of x-ray of the
breast that up until days ago was routinely promoted to Canadian women 40 and
up as an annual must-have.
But the
Canadian Task Force on Preventive Health Care has rocked the boat big-time with
new recommendations that reduce the use of mammography.
The task
force has toned down Canada’s 10-year-old guidelines around when to get
mammograms. The revised guidelines suggest routine mammograms only for women
ages 50 to 74 and even then no more than once every two or three years.
No big deal
in the grand scheme of things. One less medical appointment to schedule.
But it’s
disturbing when something that has been sold to us as an absolutely essential
health measure suddenly reveals a dark side. The about-face on mammograms
serves as an excellent reminder that health care can hurt.
In the case
of mammograms, the issue is “false positives.” Mammograms are prone to turning
up slow-growing lumps in the breast that look like cancer but in fact do no
harm over a lifetime.
That means
you can end up having surgery, radiation and chemotherapy you didn’t need - treatments
that can damage your health permanently and waste precious health-care dollars
to boot. False positives have been a major issue in prostate-cancer screening
for years now for those very reasons.
Mammograms
provide “a real benefit,” said task force chair Dr. Marcello Tonelli in media
reports this week on the revised guidelines. “But compared with the risk of
false positives, it’s relatively small. If you look at the numbers, you are
much more likely to have a false positive result than you are to have your life
saved with screening.”
New Yorker writer Malcolm Gladwell saw
this one coming years ago. He wrote a brilliant article back in 2004, “The
Picture Problem,” that detailed the challenges that even the most expert
radiologist faces when trying to decipher a mammogram image.
“Looking at a mammogram is
conceptually different from looking at images elsewhere in the body,” Memorial
Sloan-Ketterer Cancer Centre radiologist Dr. David Dershaw told Gladwell in
that piece. “Everything else has anatomy—anatomy that essentially looks the
same from one person to the next. But we don’t have that kind of standardized
information on the breast.
“The most difficult decision I
think anybody needs to make when we’re confronted with a patient is: Is this
person normal? And we have to decide that without a pattern that is reasonably
stable from individual to individual, and sometimes even without a pattern that
is the same from the left side to the right.”
The point of the article was that
humans place too much trust in pictures as revealing “truth.” The picture that
emerges from a mammogram is particularly open to interpretation.
Gladwell highlighted eye-opening
findings from the University of Washington Harborview Medical Centre as to what
happened when 10 radiologists were asked to interpret the same 150 mammograms.
One caught 85 per cent of cancers
in the images right away. Another caught 37 per cent. Some saw many things to
worry about, others saw none. In one case, three radiologists deemed a lump visible
in the image to be normal, two others saw it as abnormal but probably benign, four
weren’t sure, and one was certain it was cancerous.
Mammography does save lives. But
not many, as it turns out. If 1,000 women who are age 60 right now have an
annual (and let’s presume correctly interpreted) mammogram every year for the
next decade - 10,000 mammograms, with all the expense that entails - breast
cancer deaths among the group could be expected to drop from nine to six.
Nobody can blame us for wanting a
fail-safe test that catches cancer early. Alas, the science isn’t there yet,
and at any rate something new will likely be killing us by that point. Such is
the nature of the human condition.
Preventing breast cancer remains
important, of course. But so much of prevention comes down to personal
responsibility - for what you eat; how often you exercise; how much you weigh; your
alcohol consumption.
The world will rejoice when they
come up with a screening program that corrects for bad habits. Until then, take
care.
