Breast test results often false

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Sep. 16, 2003. 06:21 AMBreast test results often false

In mammograms, we rate poorly

Result: Higher costs and anxiety

 

 

ELAINE CAREY

MEDICAL REPORTER

 

Mammograms in Canada and the United States routinely produce more false positive

readings than those in other developed countries, according to a new study.

 

The number of mammograms deemed abnormal was 2 to 4 percentage points higher in

North America, without any corresponding increase in the number of breast

cancers detected, says the study, published today in the Journal of the National

Cancer Institute.

 

That leads to unnecessary follow-up procedures, higher medical costs and anxiety

for patients, says the study by the University of Washington's Harborview

Medical Center in Seattle. It estimates that those costs in the United States

add up to an additional $750 million (U.S.) a year.

 

The data looked at 32 studies of community-based mammogram programs in 18

countries, including 12,000 mammograms in British Columbia, which had one of the

highest false positive rates in the world.

 

Only 4.6 per cent of the Canadian women — or one in every 22 — who were told

they had an abnormal mammogram actually had cancer, a rate of false positive

tests slightly behind only those in Hong Kong, Portugal and New Mexico, the

study found.

 

Of the Canadian women who had a biopsy because of the mammogram reading, only

27.7 per cent had cancer.

 

By comparison, more than half of North Carolina women who had biopsies based on

mammograms had cancer, and more than two-thirds of those in the Netherlands, the

country with the best mammogram record.

 

" If you look at these numbers, I'd rather be in North Carolina, " said Dr.

Cornelia Baines, a professor in the department of public health sciences at the

University of Toronto.

 

" You can see the relief on a woman's face when you tell her that eight of 10

abnormal mammograms are false readings, " she said.

 

" But from a population point of view, eight out of 10 of these follow-ups are

unnecessary. "

 

The new study, by a respected research group, is " very, very sound in

documenting persuasively this is a problem that is more important in North

America than in Europe and other countries, " said Baines, a principal researcher

on the Canadian National Breast Screening Study in the 1980s.

 

" If you look at the countries and compare, you have to ask: Why are countries

like Iceland and Australia so much better than Canada? " she said. " It goes back

to the contrast between entrepreneurial medicine and population programs that

are rigorously controlled. "

 

While a number of other possible reasons are cited for the high false positive

rate, " I feel strongly this is the unfortunate impact of medical malpractice, "

said Dr. Joann Elmore, the study's lead investigator.

 

Failure to detect cancer is the number-one cause of malpractice suits in the

U.S., and breast cancer tops the list, she said in an interview. Doctors are

afraid not to order more tests for even the slightest possibility of a problem

with the mammogram.

 

" Radiologists have it tough, and primary-care doctors are also sued for failing

to follow up, " she said.

 

Baines said malpractice is also an issue in Canada, although not to the same

extent as in the U.S. " But it's still a factor any doctor would have in the back

of their mind, " she said.

 

Another factor is the quality of mammograms, which in the U.S. have been found

to be " atrocious, " she said. " There are bad mammograms done in Toronto, too, but

there are also good ones. "

 

Financial incentives built into the health care system and how different doctors

interpret the tests could be other reasons, the study suggests.

 

Even in Canada, the fee-for-service system encourages more testing, and the

Ontario and B.C. breast screening programs have been " basically persuaded that

the screening has to occur in private doctors' offices, " Baines said. Elmore

said she hypothesized that the study would find higher rates of abnormal

mammograms in North America but also that they would detect more breast cancers,

which they didn't.

 

" It would be okay if the higher recall rate gave us more bang for our buck, but

we didn't find that, " she said. " The majority of recalls were false positives. "

 

The differences persisted in the North American studies even after controlling

for the age of the women screened, the number of readers for each mammogram and

the number of pictures taken in each mammogram.

 

This isn't the first study to come up with surprising news about mammography. A

study by Toronto doctors about a year ago showed no reduction in breast cancer

death rates for women who get the screening test in their 40s.

 

And an international uproar has surged in the past year about whether routine

mammography saves lives.

 

A Swedish study in the spring of 2002 found screening healthy women for breast

cancer reduces deaths by 21 per cent, calling it a modest benefit.

 

 

 

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