Purpose: To determine the chance of malignancy in lesions classified as "probably benign" by dynamic magnetic resonance imaging (MRI), in a heterogeneous population.
Materials and methods: Reports from 473 patients, from March 1994 to March 2002, who underwent breast MRI were retrospectively reviewed. A total of 79 patients (17%) had lesions classified as probably benign after the MRI, which required further imaging follow-up. We evaluated subsequent MRI, mammographic reports, and clinical follow-up in these patients and established the frequency of malignancy in this group.
Results: MRI classified probably benign lesion were diagnosed in 79 women because of focal or diffuse mild enhancement and benign dynamic enhancement curves in the area of the mammographic abnormality, or because of the presence of microcalcifications on the mammogram, or because of incidental enhancing lesions. Two-year radiographic and/or clinical follow-up was available in 68 women. On follow-up, four women (6%) were diagnosed with cancer between 14 and 18 months after the initial MRI.
Conclusion: Patients with a lesion assessed as probably benign by dynamic contrast enhanced MRI have a higher chance of malignancy than patients with probably benign lesions (Breast Imaging Reporting and Data System category 3, BI-RADS 3) seen on mammography. These patients should be informed of the increased risk of cancer and be given the option of biopsy or close follow-up.