A recent study in the journal Radiology reports that a breast MRI, after a mammogram finds evidence of breast cancer, often detects larger and more aggressive tumors. Some of those tumors are not seen on traditional mammography.

Breast MRI is more sensitive for detecting breast cancers than mammograms, and has often been used for high-risk patients or for pre-operative planning in younger women and those with dense breasts. MRI can detect multicentric cancers, where there are two or more distinct primary tumors, which may be in different quadrants. But there has been controversy about whether the additional tumors found on MRI may lead to overtreatment and additional risks for patients.

In the Radiology study, records of more than 2,000 patients were reviewed. The patients had newly diagnosed breast cancer after mammography and were subject to biopsy after pre-operative MRI. The study found that 14% of the patients had additional cancer found on MRI that had not been seen on mammography. Of those patients, 25% had tumors in a different quadrant of the breast than those detected on mammography. Some of the newly discovered tumors were larger than those detected on mammograms and, because of their size and location, required re-assessment of planned treatment.

An author of the article about the study said that “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.”