MRI-guided breast needle core biopsies: pathologic features of newly diagnosed malignancies.

Magnetic resonance imaging (MRI) of the breast is used for select groups of patients. MRI-guided breast core needle biopsies performed over a 3-year period were retrospectively reviewed to determine the incidence and types of cancers found and to correlate the cancers with the MRI findings and the indication for the study. Patients were stratified based on indication for MRI examination including, evaluation of disease extent in patients with current ipsilateral carcinoma, surveillance for recurrence of prior ipsilateral carcinoma, as a problem-solving method and for screening high-risk patients. The high-risk screening group included those with family history (with or without germline mutations), prior chest wall radiation, and contralateral breast carcinoma (current or prior). Four-hundred and forty-five biopsies were performed on 386 patients. The majority of biopsies (79%) were benign. Biopsies demonstrating ductal carcinoma in situ (DCIS) and invasive carcinoma were more likely to present as nonmass-like and mass-forming enhancements respectively, but with only 52% specificity. The highest rate of malignancy (44%) was seen in the least frequently biopsied patient group (n = 25), those with prior ipsilateral carcinoma. Conversely, the most frequently biopsied group (n = 283), the high-risk screening group, demonstrated the lowest malignancy rate (16%). Within this group, most malignant cases were invasive carcinomas (n = 27), 67% of which were small (≤1 cm), well or moderately differentiated with a good prognostic receptor profile (estrogen receptor positive, human epidermal growth factor receptor 2 negative), and lacked nodal macrometastases. The remaining malignant cases in the high-risk screening group were DCIS with or without microinvasion (n = 18), 78% of which demonstrated high nuclear grade. Overall, enhancement pattern did not correlate with the likelihood of or type of malignancy. The most common types of carcinomas identified by screening were small estrogen receptor positive invasive tumors and high grade DCIS.