Avoiding preoperative breast MRI when conventional imaging is sufficient to stage patients eligible for breast conserving therapy.

Aim: To determine when preoperative breast MRI will not be more informative than available breast imaging and can be omitted in patients eligible for breast conserving therapy (BCT).

Methods: We performed an MRI in 685 consecutive patients with 692 invasive breast tumors and eligible for BCT based on conventional imaging and clinical examination. We explored associations between patient, tumor, and conventional imaging characteristics and similarity with MRI findings. Receiver operating characteristic (ROC) analysis was employed to compute the area under the curve (AUC).

Results: MRI and conventional breast imaging were similar in 585 of the 692 tumors (85%). At univariate analysis, age (p<0.001), negative preoperative lymph node status (p=0.011), comparable tumor diameter at mammography and at ultrasound (p=0.001), negative HER2 status (p=0.044), and absence of invasive lobular cancer (p=0.005) were significantly associated with this similarity. At multivariate analysis, these factors, except HER2 status, retained significant associations. The AUC was 0.68.

Conclusions: It is feasible to identify a subgroup of patients prior to preoperative breast MRI, who will most likely show similar results on conventional imaging as on MRI. These findings enable formulation of a practical consensus guideline to determine in which patients a preoperative breast MRI can be omitted.