Breast MRI before irradiation zeros in on remote multifocal disease

Potential candidates for accelerated partial breast irradiation may benefit from pretreatment MRI to ensure no cancer is missed, according to a study conducted by Boston-based researchers.

Dr. Juan Godinez of the radiation oncology department at Brigham and Women's Hospital and the Dana-Farber Cancer Institute and colleagues found that breast MRI reveals mammographically occult cancer foci in 38% of cases.

The retrospective study included 79 women, aged 29 to 75, all eligible for breast-conserving surgery and accelerated partial breast irradiation (APBI). Based on clinical, imaging, and pathology results, 62% of the women were considered eligible for APBI with T1-T2, N0, M0 breast cancer. MRI detected 126 abnormalities, including the index tumors.

Additional cancer sites, other than the index tumors, were found in 38% of patients. Of the 38%, 10% had additional cancer in a different quadrant from the index tumor

After lumpectomy, doctors are likely to recommend whole-breast irradiation to ensure no tumor cells are missed. The alternative, APBI, in selected patients at low risk for local recurrence is "safe and well tolerated, but long-term recurrences and cosmetic results are not yet available," according to the researchers.

APBI damages cells in a 1 to 2-cm radius around the surgical bed. Other parts of the breast may still be cancerous, however, and thus left untreated. The fact that the researchers found MRI revealed mammographically occult cancer foci in 38% of patients implies that a patient receiving APBI may not receive radiation treatment to other affected areas.

"Left nonirradiated, occult cancer may give rise to a recurrent disease that manifests years later," Godinez told Diagnostic Imaging.

The study appeared in the American Journal of Roentgenology (2008;191[7]:272-277).

"Breast MRI may provide benefit by potentially refining criteria for selecting patients for treatment with accelerated irradiation, with its ability to detect multifocality and additional tumor sites away from the lumpectomy bed," the researchers said. "MRI should be part of the workup for those patients who meet eligibility criteria for APBI and are interested in less than whole-breast irradiation."

Dr. Wendy Woodward, an assistant professor of radiation oncology at the M.D. Anderson Cancer Center in Houston, pointed out potential bias in the study.

"The referral pattern for MRI represents a bias in this study population toward young women and women with ambiguous findings on routine imaging, who are not necessarily the same patients referred for APBI," she said.

The cohort includes 13 patients who received neoadjuvant chemotherapy, making them ineligible for APBI, which may further bias these results, according to Woodward.

"Validation of these data in a cohort of women without underlying indication for MRI referral to confirm the usefulness of this modality in the general population of breast cancer patients eligible for APBI would be helpful," she said.

APBI efficacy data primarily exist for selected groups of women.

"A similar study of breast MRI among these selected groups would assist in determining the true cost-benefit ratio for MRI in APBI," Woodward said.

"It is premature to suggest that incorporation of MRI would make APBI universally acceptable for women of this cohort with single lesions," she said.

For more information from the Diagnostic Imaging archives:

MRI breast cancer staging proves benefits, shortcomings

Breast MRI CAD zeroes in on malignant lesions

Clinical support grows steadily for breast MRI