FRIDAY, Sept. 5 (Health.com) — Women with dense breasts who undergo a new type of breast cancer screening have fewer false alarms and a greater likelihood of tumor detection than they would with a mammogram, according to a study presented this week at an American Society of Clinical Oncology conference in Washington, D.C.

However, the test—called molecular breast imaging or MBI—is unlikely to be an option at annual cancer screenings in the near future. Because the test involves exposure to radiation and needs additional study, it might be more useful to women who are candidates for magnetic resonance imaging (MRI), which is generally reserved for those with a high risk of breast cancer.

MRIs don’t involve any radiation exposure, but mammograms, which are a type of X-ray, do involve a small amount of radiation. MBIs expose women to more radiation than a mammogram.

During an MBI, a radioactive tracer is injected into the body and “lights up” cancerous cells in the breast when viewed through a special camera.

“The 8- to 10-fold increase in radiation is a concern,” Debbie Saslow, PhD, director of breast and gynecologic cancer at the American Cancer Society, says of the new screening method. “The women most likely to have dense breasts are younger women, whose breasts are more susceptible to the harms of radiation.”

And Julia A. Smith, MD, PhD, a clinical assistant professor at New York University School of Medicine, asks, “What does this add? We [already] know that mammograms are of decreased efficacy in women who are high risk either because of genetics, family history, other breast disease, or breast density.”

She points out that these particular women are now being given MRIs, not mammograms, to interpret their hard-to-read tissue. “So it would be important to know how MBIs compare [to magnetic resonance imaging].”

The new findings suggest that MBIs might be less stressful than mammograms because of the lower likelihood of a false positive, a test result that seems suspicious but turns out to be nothing.

The researchers from the Mayo Clinic in Rochester, Minn., reported that mammograms led to false alarms in 9% of the patients involved in the study but in only 7% of the patients who had an MBI (the radioactive tracer occasionally binds to noncancerous tissue too).

Fewer false positives might mean cheaper medical bills because women could skip unnecessary biopsies and other tests to rule out cancer. MBIs, which cost less than $500, according to the Associated Press, are still more expensive than mammograms, though.

They do, however, cost less than MRIs, which can be more than $1,000. But without direct MBI-MRI comparisons on safety and sensitivity, it’s hard to tell how important monetary cost will be. (Results from one of the first studies putting MBI and MRI head-to-head were also presented this week in Washington.)

Then there’s the matter of MBIs and their radioactive tracers; some women are allergic to such agents. “It’s a small risk,” says Saslow, “but it’s something that makes it more complicated than a mammogram.”

For now, says Dr. Smith, mammograms, MRIs, and ultrasound are still your best bets for screening high-density breasts. “By no means should MBI be a standard of care right now,” she says. “No one should be experimenting. We don’t know what the down side is yet.”

By Sally Chew

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