Histological assessment of breast lesions identified exclusively by magnetic resonance.

Radiologic-pathologic correlation of lesions diagnosed by magnetic resonance (MR) is precluded by insufficient data on histological characteristics of lesions suspicious on MR but not visible on concurrent mammogram or ultrasound. The objective of this study was to describe histological features of breast lesions diagnosed exclusively by MR. The participants underwent MR-guided breast biopsy between 2007 and 2012 for a suspicious lesion not identified by mammography or ultrasound. Histology slides were interpreted retrospectively by a breast pathologist. Of 126 patients (126 lesions), 34 (27%) had new breast cancer, 51 (40.5%) previous breast cancer, and 41 (32.5%) dense breasts or a significant family history of breast cancer. MR identified 23 (18.3%) invasive cancers: 20 were Grade 1 and 17 were ductal. Of the 126 lesions, 16 (13%) were ductal carcinoma in situ (DCIS), four were atypical ductal hyperplasia and atypical lobular hyperplasia (3%), and 68 (54%) were benign. Fifteen biopsies (12%) had no significant pathology. Five DCIS lesions were upgraded to T1 invasive cancers. Approximately 30 per cent of suspicious lesions detected exclusively by MR are invasive or in situ cancers that are predominantly low grade. Further studies are needed to determine if malignant lesions can be prospectively distinguished by MR characteristics.