Molecular breast imaging boosts cancer detection

Volume 4, Issue 2, 2015


New imaging tool finds tumors obscured by dense breast tissue on mammograms.

Photograph of Deborah J. Rhodes, M.D.

Deborah J. Rhodes, M.D.

Photograph of Michael K. O'Connor, Ph.D.

Michael K. O'Connor, Ph.D.

A new breast imaging technique pioneered at the Mayo Clinic Cancer Center nearly quadruples detection rates of invasive breast cancers in women with dense breast tissue, according to the results of a major study published in the February 2015 issue of the American Journal of Roentgenology.

Molecular breast imaging (MBI) is a supplemental imaging technology designed to find tumors that would otherwise be obscured by surrounding dense breast tissue on a mammogram. Both tumors and dense breast tissue can appear white on a mammogram, making tumors indistinguishable from normal tissue in women with dense breasts.

About half of all women eligible for screening have dense breast tissue, said Deborah J. Rhodes, M.D., a Mayo Clinic Cancer Center physician and senior author of the published study.

Molecular breast imaging increased the detection rate of invasive breast cancers by more than 360 percent when used in addition to regular screening mammography, according to the study.

Molecular breast imaging uses small semiconductor-based gamma cameras to image the breast following injection of a radiotracer that tumors readily absorb. Unlike conventional breast imaging techniques, such as mammography and ultrasound, molecular breast imaging exploits the different behavior of tumors relative to background tissue, producing a functional image of the breast that can detect tumors not seen on mammography.

The Cancer Center study included 1,585 women with extremely dense breasts who underwent molecular breast imaging at the time of their screening mammograms. Among the findings:

  • Of these women, 21 were diagnosed with cancer — five through mammography alone (24 percent, or 3.2 cancers per 1,000 women) and 19 with mammography plus molecular breast imaging (91 percent, or 12 cancers per 1,000 women).
  • Particularly notable was the fourfold increase in detection of invasive cancers — 1.9 invasive cancers per 1,000 women with mammography versus 8.8 per 1,000 women with mammography plus molecular breast imaging. Detection rates for noninvasive cancers were not significantly different.
  • The risk of incurring an unnecessary biopsy because of a false positive exam increased in this study, from 1 in 100 women with mammography to 4 in 100 women with mammography plus molecular breast imaging.

"The finding that MBI substantially increases detection rates of invasive cancers in dense breasts without an unacceptably high increase in false positive findings has important implications for breast cancer screening decisions, particularly as 21 states now require mammography facilities to notify women about breast density and encourage discussion of supplemental screening options," Dr. Rhodes said. "These findings suggest that MBI has a more favorable balance of additional invasive cancers detected versus additional biopsies incurred relative to other supplemental screening options."

Michael K. O'Connor, Ph.D., a Mayo Clinic Cancer Center scientist and inventor of the molecular breast imaging technology, called this study a major milestone for both safety and efficacy.

"This new study is important because it incorporates many of the advances in MBI pioneered here at Mayo Clinic and shows that studies can be performed safely, with low radiation exposure to the patient," Dr. O'Connor said. "This means MBI is safe and effective as a supplemental screening tool."