RODEO Breast MRI Promising in Lobular Cancer Diagnosis

July 1, 1996

DALLAS--RODEO breast MRI proved significantly more accurate than mammography in determining the extent of lobular carcinoma and in characterizing the morphology of the disease, Steven E. Harms, MD, said at the American College of Radiology breast cancer symposium.

DALLAS--RODEO breast MRI proved significantly more accurate thanmammography in determining the extent of lobular carcinoma andin characterizing the morphology of the disease, Steven E. Harms,MD, said at the American College of Radiology breast cancer symposium.

In the Baylor study of 20 breast cancer cases with pathology proveninfiltrating lobular carcinoma, RODEO MRI findings agreed withpathology results concerning the extent of disease in 85% of casesversus 31.8% for mammography.

Although lobular carcinoma accounts for less than 10% of breastcancers, an estimated 30% of malpractice suits for failure todiagnose on mammography involve the lobular carcinoma histology.

This is because the unique infiltrative pattern of lobular carcinomamakes it difficult to palpate, and tumors may not show up on mammographyuntil the mass is very large, said Dr. Harms, director of magneticresonance imaging, Bay-lor University Medical Center, Dallas.

About one third of lobular cancers are bilateral and multifocal.Although lum-pectomy is a treatment option, mastecto-mies aremore often performed because of the inability of mammography andconventional MRI to correctly determine the extent of the diseaseprior to surgery.

Conventional MRI is problematic in this setting because of volumeaveraging, he said. "Low-contrast, low-resolution techniqueswill average out the tumor with the surrounding tissue, so thatit is below the threshold for detection."

However, RODEO (rotating delivery of excitationoff-resonance) three-dimensional MRI provides 20 times higherresolution and much better contrast than conventional MRI, Dr.Harms said.

Interobserver Agreement

The study protocol called for MRI films and mammograms to be readretrospectively by three independent blinded examiners. Interobserveragreement on the extent of disease was greater for RODEO MRI (100%vs 90.7% for mammog-raphy), as was interobserver agreement onmorphologic classification (90.7% vs 64.3%), Dr. Harms said.

The technique was 100% accurate in predicting lymphadenopathy,with no false-positives. However, three of six cases were missed.In contrast, mammog-raphy failed to detect any of the diseasedlymph nodes, he said.

Dr. Harms pointed out that no multi-quadrant breast cancer caseswere underestimated using RODEO MRI, whereas all nine multiquadrantcases were underestimated with mammography. Similarly, only onemultifocal case was under-estimated with MRI vs six of eight caseswith mammography.

MRI overestimated the extent of disease in only two patients,which is important, Dr. Harms said, in light of MRI's historyof producing false-positive results.

Based on these results, Dr. Harms believes that RODEO MRI canplay a role in the diagnosis of lobular carcinoma and in preoperativetreatment planning, especially when breast-conserving surgeryis an option.