LOS ANGELES—Breast MRI identifies mammographically occult secondary tumors in about 6% of women with early-stage breast cancer who would otherwise qualify for partial breast irradiation, Rahul D. Tendulkar, MD, a radiation oncologist at the Cleveland Clinic, reported at the 49th annual meeting of ASTRO (abstract 41).

"Breast MRI is a sensitive tool for the evaluation of disease extent in comparison with mammography, and at our institution, the majority of patients with a new diagnosis of invasive breast cancer or DCIS nonselectively undergo pretreatment bilateral breast MRI," Dr. Tendulkar said.

To assess whether this modality can help guide the selection of appropriate patients for PBI, he and his colleagues retrospectively studied the incidence of MRI-detected secondary tumors in 260 consecutive patients who met the trial eligibility criteria (based on mammography, ultrasound, physical examination, and surgical pathology) and underwent a dynamic, contrast-enhanced MRI read by a dedicated breast radiologist using computer-aided detection. Targeted ultrasound with or without biopsy was used to further evaluate any MRI-identified suspicious lesions.

Additional lesions detected

MRI detected suspicious additional lesions in 20% of the patients, and on the basis of the results of targeted ultrasound imaging, 10% underwent a biopsy of these lesions, Dr. Tendulkar reported.

Overall, MRI identified biopsy-proven, mammographically occult secondary tumors in 15 (5.8%) of the patients; the tumors were ipsilateral in 4.2% and contralateral in 1.5% (see the Figure on page 40).

The overall finding of 5.8% mammographically occult breast cancers "may represent a baseline incidence in this relatively unselected population of women with early breast cancer," Dr. Tendulkar commented at the meeting.

The rate of ipsilateral secondary tumors was significantly higher in patients whose primaries were infiltrating lobular carcinoma (ILC), compared with tumors of other histologies (18% vs 3%).