Pathologic Characterization of Non-Mass Enhancement Lesions of the Breast in MRI-guided Biopsy.

OBJECTIVE: Breast MRI is widely used for screening high-risk patients and for assessing the extent of disease in patients with breast cancer. The goal of this study was to determine the pathologic findings associated with MRI-guided core needle biopsies performed for non-mass enhancement (NME) lesions of the breast. METHODS: We retrospectively identified 270 MRI-guided core needle biopsies from 225 women performed at our institution between January 1, 2024, and Dec 30, 2025. All included cases demonstrated non-mass enhancement on MRI. Radiologic and pathologic findings were reviewed. Cases were divided into two groups: those with a recent diagnosis of ipsilateral malignancy (n = 74) and those without a recent diagnosis of malignancy (n =196). RESULTS: Biopsies from patients with a known ipsilateral malignancy demonstrated a higher frequency of invasive carcinoma (20% vs. 7%, p = 0.003) and in situ carcinoma (27% vs. 9%, p =0.0002) compared with those without ipsilateral malignancy, and a lower frequency of benign findings (46% vs. 77%, p = 0.0001). NME-associated invasive carcinomas were predominantly well- to moderately-differentiated carcinomas (96%) and were ER-positive/HER2-negative (>90%). NME-associated DCIS were 57% high grade, 43% intermediate grade, with 36% showing an ER-negative staining. CONCLUSION: MRI-guided biopsies for NME lesions demonstrate a significant rate of malignancy, particularly in patients with known ipsilateral breast cancer. Most NME-associated malignancies are well- to moderately-differentiated, hormone receptor-positive/HER2-negative carcinomas, while a subset of high-grade, ER-negative DCIS highlights the heterogeneous nature of these lesions.