The accuracy of incremental pre-operative breast MRI findings - Concordance with histopathology in the Swedish randomized multicenter POMB trial.

Purpose: The Pre-Operative MRI of the Breast (POMB) trial was a randomized, prospective, multicenter trial evaluating the impact of pre-operative breast MRI on treatment regimens and short-term surgical outcomes in women up to 56 years of age with breast cancer. The purpose of this study was to evaluate the performance of pre-operative breast MRI in the POMB trial with respect to incremental MRI findings - over conventional breast imaging methods - and their concordance with histopathology.

Patients And Methods: Two-hundred and ten patients (n = 210) participating in the POMB trial underwent pre-operative breast MRI at two Swedish breast units. Positive predictive values (PPV) for the incremental MRI findings were calculated for three subgroups of patients with: 1. alteration/alterations of treatment plan; 2. no alteration of treatment plan; and, 3. MRI-related conversion from BCS to mastectomy. Area under the receiver operating characteristic curve (AUC) was calculated using in-breast BI-RADS based ratings for the whole MRI group.

Results: After exclusions a total number of 99 incremental findings in 78 patients were eligible for statistical analysis resulting in a PPV = 74%: (95% CI 60-84%) in 39 patients with MRI related alterations of initial treatment plans and 27%: (95% CI 14-44%) in 39 patients without. Positive predictive values of incremental findings decisive for specific treatment alteration/s were 83% (95% CI 68-92%) in patients with any alteration of initial treatment plans and 91% (95% CI 70-98%) for patients (n = 20/22) with conversion from breast conserving surgery to mastectomy. The empirical AUC for the incremental findings in the whole MRI group was 85% (95% CI 78-91%).

Conclusion: Breast MRI, performed and evaluated together with conventional breast imaging methods can provide relevant information at a high degree of accuracy in the pre-operative setting.