Ultrasound Improves Detection of Breast Cancer
Researchers affiliated with the American College of Radiology Imaging Network (ACRIN) trial have reported that the addition of ultrasound to mammography significantly increases the number of breast cancers detected in high-risk women but also increases the number of false-positive tests. The details of this randomized study appeared in the May 14, 2008 issue of the Journal of the American Medical Association.1
Mammography is the routine method for detecting early breast cancer, although the combination of ultrasound and MRI is thought to be more accurate. Both techniques, however, are associated with a higher rate of false-positives and increase the rate of biopsies for benign lesions.
The current study compared conventional mammography to conventional mammography plus ultrasound in 2,809 women at high risk of breast cancer due to dense breast tissue. This was a multicenter randomized trial that evaluated the number of breast cancers detected in each group and the number of breast cancers occurring in the first 12 months after testing. Forty-one breast cancers in 40 women were detected in this study:
* Eight were suspicious on both ultrasound and mammography.
* 12 were suspicious on ultrasound only.
* 12 were suspicious on mammography only.
* Nine cancers were not detected by either technique.
* Diagnostic yield was 7.6 per 1000 women screened (20 of 2637) by mammography.
* Diagnostic yield was 11.8 per 1000 women screened (31 of 2637) mammography and ultrasound.
* Diagnostic accuracy was increased from 0.78 to 0.91 when ultrasound was added to mammography.
* Diagnostic accuracy of biopsy was 19 of 84 for mammography.
* Diagnostic accuracy of biopsy was 21 of 276 for mammography plus ultrasound.
* The sensitivity of mammography for detecting breast cancer was 49% compared with 77.5% for mammography plus ultrasound.
These authors concluded that ultrasound increased diagnostic accuracy but also increased the number of false-positives.
Comments: This study points out the inadequacy of mammography in detecting early breast cancer. It is not reassuring to know that half of all breast cancers are missed by screening mammography and that a quarter are missed by combined testing. Cancer was detected in only 8.6% of patients who had a biopsy based on suspicious ultrasound. An accompanying editorial discusses the state of knowledge about breast cancer screening by mammography, ultrasound, and MRI (which appears to be the more accurate technique, but is also associated with a high false-positive rate).2 The general conclusion is that any technique that improves detection will be associated with an increased number of false-positive biopsies.
