Jury still out on ultrasound for breast cancer screening
Jury still out on ultrasound for breast cancer screening
New techniques could boost accuracy
Numerous trials have shown that ultrasound offers certain advantages over other imaging technologies in determining whether some lesions are cancerous. However, data presented thus far are less convincing when ultrasound is used as a screening methodology.
The latest evidence in this regard involves first-year findings from a three-year study that is looking into the value of adding ultrasound to mammography in women at high-risk for breast cancer. The findings, which were presented last fall at the American College of Radiology's meeting, leave a murky picture on whether ultrasound screening provides enough added benefit in finding additional cancers to outweigh a substantial false-positive rate.
In the study, being carried out by the American College of Radiology Imaging Network (ACRIN) with support from the Avon Foundation and the National Cancer Institute, 2,637 women received both mammography and ultrasound exams by physicians who had received special training in breast ultrasound screening. In the group of study participants, 40 women were found to have 41 breast cancers by one or both of the screening methodologies, and 12 of the cancers were found by ultrasound alone. However, the addition of ultrasound also resulted in 136 women having biopsies for suspicious lesions, but only 14 of these women were found to have breast cancer.
From these findings, investigators conclude that adding ultrasound to mammography will find one to seven cancers in 1,000 high-risk women who have not previously been screened by ultrasound. However, it will also substantially increase the false-positive rate. The principal investigator of the study, Wendie Berg, MD, PhD, FACR, a breast imaging consultant at American Radiology Services, Johns Hopkins Greenspring Station in Lutherville, MD, declined to discuss the specifics of the findings prior to publication, but she emphasizes that these results are just for the first prevalent screen. "Two years from now, we will have results to report regarding the role of annual supplemental ultrasound screening," Berg says.
In a 1999 study into the value of ultrasound as an adjunct to mammography, investigators concluded that ultrasound offers improved cancer detection in women with dense breasts. However that study, conducted by Thomas Kolb, MD, a radiologist in private practice in New York, and colleagues, did not consider false positives.1 Kolb suggested that confirmation studies were needed before recommending the routine use of mammography and ultrasound for screening.
Since that time, ultrasound technologies have continued to advance, and new tools are emerging that show promise in improving sensitivity and specificity. For example, a technique called elasticity imaging could significantly cut down on the number of false-positive results from ultrasound screening examinations, according to Robert Barr, MD, PhD, a professor of radiology at Northeastern Ohio Universities College of Medicine in Rootstown, OH. Barr has conducted smaller studies on the technique, and is now involved in a multi-center trial.
"At this point in time, according to the American Cancer Society, 80% of the biopsies done in the U.S. are benign, and we think we can probably halve the number of breast biopsies done using this technique without too much of a problem, according to my numbers," says Barr. He explains that the technique helps to differentiate soft lesions, which are usually benign, from hard, cancerous lesions. Consider the example of a bowl of gelatin with a marble inside, he says. If you pushed on the gelatin, you would change the shape of the gelatin, but you would not change the shape of the marble, says Barr, who notes that this response is basically the same as elasticity imaging software. "As the breast moves from just normal respiration, the software [captures] how the tissues change," he says.
The elasticity reading is conducted as part of a standard ultrasound exam, explains Barr. However, in addition to the imaging information that the examiner typically receives, there is also a picture or an elastigram that shows how the tissues are moving. Further, in addition to gathering insight into the softness or hardness of a lesion, the elastigram reveals other important information as well. "What we found in our study is that cancers appear the same size or larger on the elastigram than they do on standard imaging," says Barr. "Benign lesions appear smaller."
While the software, eSie Touch Elasticity Imaging, which is made by Siemens Medical Solutions based in Malvern, PA, is already on the market, additional technical advances are needed before it can be used for screening. Further, it can only be used with Siemens ultrasound systems. The cost of implementing the software on to an existing system varies from $15,000 to $20,000, depending on which system the user has and what upgrades may be necessary, according to Siemens. Barr cautions that there is a learning curve involved with mastering the technology. "It is easy to do, but you have to do it right," he says.
Reference
- Jefferson T. Ultrasound may markedly improve cancer detection in dense breasts. JAMA 1999; 281:311-312.
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