LAUSR

BACKGROUND Breast MRI has been associated with significant rates of false positive findings. We aimed to determine the frequency of extra-mammary findings (EMFs) in newly diagnosed breast cancer patients on breast MRI with contrast and assess the significance of these findings and need for additional imaging and follow up. STUDY DESIGN Retrospective review of patients diagnosed with breast cancer from October 2018 - October 2019 was performed. Clinico-pathologic features were collected, including type of breast cancer, size, stage, and whether the patients had a breast MRI. Those who had MRI were included and MRI was reviewed to determine if EMFs were identified. Further imaging and follow up were assessed and recorded. RESULTS Of the 480 patients included in this cohort, 353 (74%) had invasive cancer while the remainder had DCIS. Two hundred and ninety patients (60%) underwent MRI, and 53/290 (18%) had EMFs on MRI. Of these, 28/53 (53%) underwent additional imaging to further evaluate findings. Two invasive procedures were performed (fine needle aspiration and thymectomy), and one malignancy was identified in the thymus. No metastatic breast cancer was identified in any patient. CONCLUSIONS MRIs are frequently obtained for newly diagnosed breast cancer patients, and additional findings, especially extra-mammary, can be stressful for patients, and potentially lead to treatment delay if further evaluation is warranted. Our results demonstrate that incidental EMFs discovered via breast MRI are common and often lead to additional imaging studies. However, no metastatic lesions were found and only one separate malignancy was identified which did not affect breast cancer management. In patients with early-stage breast cancer, EMFs yield a very low rate of malignancy, providing high levels of reassurance and supporting the option of proceeding with surgery or treatment without delay.