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A false-positive diagnosis can add unnecessary anxiety and lead to invasive tests and treatments.FRANKA BRUNS

Combining clinical breast examinations with mammography catches breast cancers that mammograms miss, but also increases the number of false-positive readings, a new study has found.

Researchers have long debated the benefit of performing clinical breast exams on women who already have annual mammograms.

But the study, published online yesterday in the Journal of the National Cancer Institute, suggests that the benefit of additional screening may be overshadowed by the risk of false alarms that can lead to unnecessary anxiety and invasive follow-up treatments.

"The benefit in increased sensitivity from the addition of CBE to mammography must be weighed against potential risks and costs of further follow-up due to false-positive results as well as the anxiety associated with additional diagnostic evaluations," the authors write.

Researchers at the University of Toronto and Cancer Care Ontario compared the results of 290,000 women aged 50-69 tested at regional and affiliated centres within the Ontario Breast Screening Program between 2002 and 2003. Some received only mammograms, while others received both mammograms and clinical breast exams by specially trained, experienced nurse.

The clinical exams lasted between eight and 10 minutes and nurses used physical palpations as well as visual observations to examine breast tissue and surrounding nodes in multiple positions.

The researchers found that women who were screened at centres that offered clinical exams in addition to mammography were statistically more likely to be referred for follow-up care, with 0.4 additional cancers detected for every 1,000 women screened using the combination method.

But women who received both mammograms and clinical exams also had significantly more false-positive results, with an increase of 2.2 per cent.

That means that for every 10,000 women screened, clinical exams would reveal breast cancer in four women whose cancer would have been missed by a mammogram. But 219 women without cancer would also receive false-positive results.

That's a whopping 55 false alarms for each additional cancer detected.

Receiving a false-positive screening can be a terrifying ordeal for women, as they are forced to undergo more testing and wait weeks for results. Previous studies have shown that the effects of this anxiety can last for months or even years.

Doctors may also recommend unnecessary and invasive biopsies, which can be painful and cause permanent scarring.

Anna M. Chiarelli of Cancer Care Ontario, who co-authored the study, said that it's too early to determine whether or not clinical exams should be abandoned.

But she said that women need to be informed about the benefits and limitations of adding clinical exams to mammography. Once they know the facts, she said, it's up to them to decide whether the additional screening is worth the possible risk.

In an editorial accompanying the paper, Joann G. Elmore, a physician and professor at the University of Washington School of Medicine, agreed that making any conclusions about the value of adding clinical examination to mammography is premature.

"We like things black and white," she said. But she added: "I don't think we'll ever have a clear answer."

Still, Dr. Elmore said that doctors need to do a much better job educating women about the benefits of different cancer screening methods, even when time is limited.

Doctors can also prepare patients for the possibility of a false-alarm, which can help reduce – if not eliminate – anxiety if the patient is flagged for further testing.

In the U.S., she noted, at least 50 per cent of women who have an annual mammogram screening over a decade will receive at least one false positive reading.

"I want them to know that this is a part of screening and it is very common." she said.

"People assume that women know," but they don't.