Breast Cancer Detection in Screening Mammography Improved Over Time

Whereas recall rates increased, the increase in cancer detection rates outweighed the increase in false-positive findings, according to researchers. This is the first study to provide long-term radiologist performance measures in a large sample of U.S. women undergoing screening mammography.

Researchers analyzing 2.5 million screening mammograms performed on nearly one million women found discrimination of cancerous from noncancerous lesions improved over a nine-year period. Results of the study were published in May 2010 the online edition of the journal Radiology. "To our knowledge, this is the first study of time trends for performance measures in a large representative sample of women undergoing screening mammography in the United States,” said lead author Laura E. Ichikawa, M.S., biostatistician at the Group Health Research Institute in Seattle, WA, USA).

The researchers examined data from six mammography registries in the Breast Cancer Surveillance Consortium. The data included 2,542,049 screening mammograms of 971,364 women (age 40 to 79) performed at healthcare facilities throughout the country between 1996 and 2004.

Each of the women included in the study had at least one prior mammogram and at least nine months in between mammography exams. Cancer registries and pathology databases were used to identify breast cancers that occurred within one year of any mammogram included in the study. "We found universal trends that breast imagers are increasing their ability to detect and intercept breast cancer before a lump is felt by a woman,” said study coauthor R. James Brenner, M.D., professor of clinical radiology at the University of California, San Francisco (UCSF; USA).

Analysis of the radiologists' performance in interpreting the mammograms over the nine-year time period showed an increase in the recall rate, or mammograms resulting in patients being called back for further evaluation, from 6.7% (10,779 of 160,329 mammograms) in 1996 to 8.6% (24,630 of 285,286) in 2004.

The sensitivity rate (ability of radiologists to identify cancer when present) increased from 71.4% in 1996 to 83.8% in 2004. The specificity rate (level to which radiologists accurately identified noncancerous lesions) decreased from 93.6% in 1996 to 91.7% in 2004.

According to Dr. Ichikawa, the increase in the cancer detection rate outweighed the increase in false-positive test results over the nine-year time period, for a positive net effect. "This is good news for women and for radiology that we have seen a net improvement in how radiologists interpret mammograms,” she said. "Radiologists are doing a better job of discriminating cancer from noncancer.”

A total of 12,498 invasive cancers and noninvasive tumors were diagnosed. An invasive cancer is a cancer that has metastasized beyond the layer of tissue where it developed and is growing into surrounding, healthy tissues. Overall, 78.7% of tumors included in the study were invasive.

The majority of mammograms included in the study were film studies. According to Dr. Ichikawa, future studies should focus on time trends of radiologists' interpretive performance when reading digital mammograms. Digital mammography, which was just beginning to be adopted in healthcare institutions towards the end of this study, is now available in approximately half of all mammography facilities in the United States.

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Group Health Research Institute
University of California, San Francisco