Additional breast cancers found with magnetic resonance imaging (MRI) are sometimes larger and potentially more aggressive than those found on mammography, according to a study in Radiology (doi:10.1148/radiol.2015150796). Researchers said that, in some cases, additional cancers found on MRI and not seen on mammography may necessitate a change in the treatment plan.

Breast MRI is the most sensitive technique for the detection of breast cancer, with widespread application in the screening of high-risk patients and presurgical planning. In younger women and women with dense breasts, MRI is effective in the detection of what are known as multicentric cancers, meaning breast cancers involving 2 or more distinct primary tumors, usually in different quadrants of the breast. However, there has been some debate about the clinical significance of multicentric cancers found with MRI.

“Patients with clinically insignificant cancers undergoing potential overtreatment versus patients who may be undertreated is at the heart of the controversy surrounding breast MRI,” said the study’s lead author Chiara Iacconi, MD, from the Breast Unit at USL1 Massa-Carrara in Carrara, Italy.

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To learn more, Iacconi and colleagues reviewed records from 2021 patients with newly diagnosed breast cancer who underwent biopsy after preoperative MRI. Additional cancer that was hidden from view on mammography was detected on MRI in 285 (14%) patients.

At least 1 additional cancer was identified on MRI in 73 (25.6%) of those 285 patients. The additional cancer was found in a different quadrant from the index cancer detected by mammography and/or breast palpation.

These multicentric cancers were larger than the known index cancer in 17 (23.3%) of the 73 patients. In addition, the size of the MRI-detected multicentric cancers was more than 1 cm in 25% of the 73 patients.

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

The additional MRI-detected multicentric cancers were found mostly in patients with heterogeneously dense or extremely dense breasts. However, additional disease was also detected on MRI in 19% 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,” Iacconi said.