The Influence of Breast Density on Preoperative MRI Findings and Outcome in Patients with a Known Diagnosis of Breast Cancer

Background: The role of breast density as an indication for preoperative breast magnetic resonance imaging (MRI) for surgical planning in women with breast cancer is unknown. Methods: We retrospectively reviewed breast cancer patients diagnosed from 2007 to 2011 who underwent preoperative MRI. We obtained clinical and pathological data and grouped patients by mammographic breast density, with Breast Imaging Reporting and Data System (BI-RADS) density A and B considered low density, and C and D considered high density. We analyzed local recurrence rates by breast density. Results: Among 683 patients, 66.6% had high breast density. We noted MRI abnormalities in the ipsilateral breast in 41.8% high-density and 30.7% low-density breasts, while contralateral abnormalities were noted in 24.9% high-density and 13.8% low-density breasts. Biopsy was recommended for MRI findings in a similar number of patients regardless of density cohort. While more abnormalities were found in high-density breasts, the rate of additional cancer found was not significantly different (ipsilateral: 32 vs. 23%; contralateral: 6.2 vs. 3.2%) for high-and low-density patients, respectively (both p > 0.15). With a median follow-up of 89 months, and similar rates of adjuvant systemic and radiation therapy, no difference in local recurrence rates existed when stratified according to density classification (p > 0.53). Conclusion: While more abnormalities were identified on MRI in dense breasts, there was no statistically significant difference in the number of cancers identified or in recurrence rates. These findings question the routine use of preoperative breast MRI in women with newly diagnosed breast cancer based solely on breast density.