Background The size and focality of the primary tumor in breast cancer (BC) influence therapeutic decision making. The purpose of this study was to evaluate whether preoperative breast magnetic resonance imaging (MRI) is helpful for the assessment of tumor size and surgical planning in early BC. Methods We performed a retrospective review of a prospectively collected database of 174 patients treated at a single institution for invasive BC who had complete documentation of the tumor size from mammography (MMG), ultrasonography (US), and MRI. Results A total of 186 breast tumors were analyzed. Mean tumor size varied by imaging method: 14.7 mm by MMG, 13.8 mm by US, and 17.9 mm by MRI. The concordance between breast imaging techniques (BIT) and final pathology with a cutoff ≤ 2 mm was 34.8% for MRI, 32.1% for US, and 27.2% for MMG. US and MMG underestimated while MRI and MMG overestimated the real tumor size. Concordance was the same in premenopausal women for MRI and US at 35%, while concordance was higher in postmenopausal women for MRI. Correlations between size determined by BIT and histopathological size were best with MRI (0.59), compared to US (0.56) or MMG (0.42). Intrinsic subtypes of BC had different concordances according to imaging method, but no significant associations were found. MRI examination revealed additional lesions in 13.8% of patients, 69% of these lesions were malignant. MRI changed the surgical plan in 15 patients (8.6%), and the rate of mastectomy increased by 6.9%. Conclusions MRI estimates BC tumor size more accurately than US or MMG, but a significant overestimation exists. Complementary MRI examination improved the concordance for tumor size between BIT and final pathology in 16.7%. MRI did not alter surgical planning for most patients and allowed more appropriate treatment for 8% of them.
