When breast MRI is performed after mammography, bigger and potentially more aggressive cancers are sometimes found, according to a new study published online in the journal Radiology. For some patients, that may lead to a change in treatment.

Breast MR is the most sensitive method for detecting breast cancer and it is widely used for screening high-risk patients and for pre-surgical planning. MR is especially effective in detecting multicentric cancers, which are cancers with two or more distinct primary tumors typically in different quadrants of the breast, in younger women and women with dense breasts.

But there is some controversy surrounding the clinical importance of those multicentric cancers. "Patients with clinically insignificant cancers undergoing potential overtreatment versus patients who may be undertreated is at the heart of the controversy surrounding breast MRI," Dr. Chiara Iacconi, the study’s lead author said in a statement.
Dr. Iacconi and her fellow researchers evaluated records from 2,021 patients with newly diagnosed breast cancer who had a biopsy after a preoperative MR exam. Out of those patients, 285 had additional cancer detected by MR that could not be seen with mammography.

MR revealed that 73 out of the 285 patients had at least one additional cancer in a different quadrant of the breast than the index cancer or the cancer detected by mammography and/or breast palpation. In addition, the multicentric cancers were larger than the known index cancer in 17 out of the 73 cases and they were greater than one centimeter in size in 25 cases.

"We believe invasive cancer larger than 1 centimeter is clinically relevant disease," said Iacconi. "In general, it is accepted that radiation can likely treat invasive cancer less than 1 centimeter, but lesions larger than 1 centimeter, especially invasive carcinomas, may not be reliably treated with conservation."

The multicentric cancers were mostly detected in patients with heterogeneously dense or extremely dense breasts, but MR also found additional disease in 19 percent of patients with fatty or scattered fibroglandular tissue.

"The results show that multicentric cancer detected on breast MRI after mammography appears to represent a larger tumor burden in approximately a quarter of patients, and can result in potential changes to cancer grade and treatment," said Iacconi.

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