Adding a clinical breast exam to screening mammography increases breast cancer detection rates, but it also increases rates of falsely positive results, Canadian researchers report in the Journal of the National Cancer Institute.

The high number of “false-positives” is a “steep price” to pay for the potential gains of adding clinical breast examination to mammography, experts not involved with the study contend in a related commentary.

For a theoretical population of 10,000 women, they explain, the addition of clinical breast examination would lead to the detection of breast cancer in only four women whose cancer would be missed by screening mammography.

However, adding clinical breast examination would also lead to false-positive results for an additional 219 women.

There is controversy about whether adding clinical breast examination to mammography improves the accuracy of breast screening.

To investigate, Dr. Anna M. Chiarelli, at the University of Toronto, and fellow researchers

compared the results of breast cancer screening with and without clinical breast exams, which in all cases were done by specially trained nurses.

The study involved 232,515 women who were screened in 2002 or 2003 by both modalities, and 57,715 who had mammography alone in the same time period at centers that did not offer clinical breast exams.

Breast cancer detection rates were higher in mammography centers that offered clinical breast examination in addition to mammography, Chiarelli and colleagues found.

Roughly 7.5 cancers were detected per 1000 women with breast exam and mammography compared with 5.4 cancers without breast exam.

However, the two techniques together also yielded a higher false positive rate compared to mammography alone: 12.5 percent versus 7.4 percent. They also resulted in more referrals for additional testing.

“Women should be informed of the risks and benefits of having a clinical breast examination in addition to mammography for breast screening,” the investigators conclude.

In a related editorial, Dr. Mary B. Barton, at the Agency for Healthcare Research and Quality in Rockville, Maryland, and Dr. Joann G. Elmore of the University of Washington School of Medicine in Seattle, remark that more needs to be known about “the role of clinical breast examination in breast cancer screening before definitive recommendations for or against its use can be made.”

SOURCE: Journal of the National Cancer Institute, online August 31, 2009.