Sophistication of breast ultrasound continues to grow

For nearly a decade, radiologists have used breast ultrasound as an adjunct to x-ray mammography to avoid unnecessary biopsies in equivocal cancer cases. Now ultrasound innovations that increase image resolution while decreasing operator dependence are reflected in a study published in the July issue of Radiology.

Researchers found that nonpalpable solid breast masses that are obscured by dense tissue during x-ray mammography but diagnosed as probably benign can be safely monitored with ultrasound instead of evaluated with biopsy. The investigators reported from the Ambulatory Care Center (ACC) in Steyr, Austria, the Medical University of Vienna, and the University of California, San Francisco.

While some radiologists now suggest both screening techniques for women with dense breasts, results have been difficult to interpret because lesions identified by ultrasound may be suspect but not dangerous. Biopsy has been recommended to confirm the status of these lesions, but this invasive procedure is often unnecessary. According to the American Cancer Society, 80% of breast lesions that are biopsied turn out to be benign.

The American College of Radiology recently introduced the Breast Imaging Reporting and Data System lexicon for ultrasound. BI-RADS classifies a solid mass with circumscribed margins, oval shape, and parallel orientation as probably benign (category 3), meaning the lesion has a very low chance of being malignant.

In the multicenter study of 409 women, researchers identified 448 nonpalpable solid masses classified by BI-RADS as probably benign at initial ultrasound. The masses were obscured by dense fibroglandular tissue. Biopsy was performed on three of these masses, and they were shown to be benign. The other 445 were followed up every six months over two to five years. Of the 445, 442 remained stable throughout follow-up. Two masses increased in size, but biopsy found them to be benign. Only one mass became palpable with cancer (diagnosed at biopsy), putting the false-negative rate at 0.2%.

"Our study shows that following a lesion with morphologic signs classified in the BI-RADS lexicon as category 3 (probably benign) is a safe alternative to immediate biopsy," said author Dr. Oswald Graf, chair of radiology at the ACC in Steyr. "When the lesion is stable at follow-up, biopsy can be averted. But it is essential that lesions strictly meet these criteria. The chance that such a lesion is malignant is not zero, but very low. For those women for whom the perceived level of risk is still unacceptable, we recommend biopsy."

Although more research needs to be conducted to support these findings, Dr. Carol H. Lee, chair of the American College of Radiology Breast Imaging Commission and a professor of diagnostic radiology at Yale University School of Medicine foresees that this screening procedure could eventually become accepted clinical practice.

Lee said she was intrigued by the study. It suggests that radiologists can use follow-up ultrasound rather than biopsy as long as the mass is nonpalpable, has all the benign characteristics, and lacks worrisome mammographic features.

"Breast ultrasound has really evolved over time," she said. "The feeling was that most solid masses that you saw on ultrasound needed to biopsied. Now we are realizing that you can apply certain sonographic criteria to masses just like we've been applying mammographic criteria to masses for years. That can help us determine with a high degree of confidence that this mass is probably benign."

For more information from the Diagnostic Imaging archive:

College, society drop out of surgeon-sponsored breast ultrasound accreditation program

Strain imaging identifies benign breast masses without biopsy

Quality issue must move beyond mammography