MBI Shows Promise in Women with Dense Breast Tissue and Increased Risk

Molecular breast imaging (MBI) has promise as an adjunct test for some women, according to a recent study, comparing MBI to mammography with the goal of establishing an additional detection tool for women with dense breasts who are at higher risk of developing breast cancer.

Carrie B. Hruska, M.D., Ph.D. Mayo Clinic

The study, presented earlier this year at an American Society of Clinical Oncology symposium, showed that MBI—a new method of breast imaging using a dedicated breast camera—performed strongly. Results showed that specially designed MBI cameras revealed more tumors and produced fewer false alarms, but researchers emphasized that the experimental technology will not replace mammograms for any women.

"At this time we think mammography works well in most women, so we see this as an adjunct for women whom mammography doesn't serve well," said Carrie B. Hruska, M.D., Ph.D., the study's lead author. "One of the benefits of mammography is that it detects microcalcifications. We are not yet sure that MBI can do that."

Dr. Hruska, a post-doctoral research fellow in the Department of Radiology at the Mayo Clinic in Rochester, Minn., said the study's initial enrollment included 1,000 asymptomatic women presenting for their annual mammogram.

The American Cancer Society, American College of Radiology and American College of Surgeons recommend that women over 40 have annual mammograms. About one-quarter of women aged 40 and older have dense breasts.

"To be included in the study the women had to have dense breast tissue, more than 50 percent dense, and another risk factor such as family history, personal history, BRCA mutation or something that elevated their risk even further," said Dr. Hruska. All participants had both tests within 21 days of one another and the reviewers read independently without knowledge of the outcome of the other test.

Technology also Yielded Fewer False Positives

Dr. Hruska said 13 tumors were detected in 12 patients—eight by MBI alone, one by mammography alone, two by both methods and two by neither.

Researchers at Mayo Clinic studied molecular breast imaging (MBI) in 12 patients with more than 50 percent dense tissue and another breast cancer risk factor such as family history, personal history or BRCA mutation. Thirteen tumors were detected in 12 patients—eight by MBI alone, one by mammography alone, two by both methods and two by neither. MBI also yielded fewer false positives and a higher positive predictive value than mammography. Researchers, who recently began a 15-month follow-up, believe the results show the promise of MBI as an adjunct test for women with dense breasts, but emphasize that MBI will not replace mammography in any women.

"Having 10 cancers picked up with MBI and only three with screening mammography was our main finding, but we also had a lot of other encouraging findings," said Dr. Hruska. "We had fewer false positives with this technology. A technique can be highly sensitive, but if it's picking up things that aren't cancer, it isn't very useful."

Researchers noted that MBI also had a higher positive predictive value than mammography. The study began in September 2005 and researchers recently began a 15-month follow-up. Researchers extended the follow-up from 12 to 15 months because many women are late scheduling their annual mammograms.

"It's important to do a follow-up because we can look at what was detected at the time of the study, but we don't know if we missed something on both modalities," Dr. Hruska said. "We have to see if anything crops up in the next year and that could affect our data. We aren't re-testing them with MBI, but we are using any other clinical findings they may have."

So far, three cancers have been detected during the follow-up period. The cancers were very small, said Dr. Hruska, and therefore it's debatable whether or not they were present at the time of the study.

While the study results are promising, said Dr. Hruska, the use of MBI in breast imaging is still in the research stages.

"We are using cadmium zinc telluride (CZT), which is a new type of gamma ray detector," she said. "With these cameras, we are able to detect very small lesions. They are specifically designed for the breast and don't have a dead space around the edge, so the breast can be placed right on the camera. By moving in so close to the breast, we can detect very small cancers."

Researchers took commercially available detectors and configured them into a dual-head breast imaging unit for their own prototype design, Dr. Hruska said.

MBI: A Cost-effective Option for Moderate Risk Women?

Jennifer A. Harvey, M.D., a professor of radiology at the University of Virginia Health Sciences Center in Charlottesville, said the study is very promising.

"MBI has been around for awhile but has not been well utilized or popular because it has traditionally been done with a gamma camera for whole-body imaging and the resolution was poor," said Dr. Harvey, who chairs the breast imaging subcommittee of the RSNA Scientific Program Committee.

"The development of gamma cameras that are smaller and get closer to the breast is where we are going to be able to see more cancers and smaller cancers," said Dr. Harvey. "The survival rates and treatment will be much better if the disease can be found at its earliest point."

While the study included 1,000 women, both Drs. Hruska and Harvey would like to see even larger studies done using MBI.

"Studies need to be done with these breast-specific cameras to compare breast cancer detection in high-risk women and in women who are more moderate risk," Dr. Harvey said. "High-risk women will probably get MR imaging because it's more cost-effective for women who are genetic carriers. But for women who are at elevated but not the highest risk, tests like this are going to be great because they will likely be more cost-effective."

The lower cost will be a huge benefit should MBI be validated and become a screening technology, said Dr. Hruska. "Other screenings used to address the limitations of mammography, like breast MR imaging, are very expensive," she said. "MBI is three to five times less costly than MR imaging, but we are still studying to see if it can do as well as MR imaging in certain applications.

"Overall, so far, we are pleased with the results of this study and we are encouraged that MBI picked up more than three times as many cancers as the screening mammogram did in women who are at increased risk and have dense breasts," Dr. Hruska concluded.