Table 1.

Potential benefits and harms of preoperative MRI.

Factor	Potential Benefits	Potential Harms
High Sensitivity	MRI is not impacted by breast density, which limits the sensitivity of mammography. Higher cancer detection rates with MRI than mammography, with greater ability to detect occult cancer in the ipsilateral breast with multifocal and multicentric disease. More accurate staging of the contralateral breast reduces the rate of breast cancer detected in follow-up. Allows the detection of all cancerous lesions at the start so they can be treated at one time instead of having pre-existing cancers only detected on short-term follow-up; this can have cost benefits for patients and the health care system, reduce anxiety, and improve the quality of life of patients. Confirmation of limited disease may allow for more conservative treatment such as partial breast irradiation (including in patients with previous radiotherapy) or the omission of systemic therapy. May allow a longer interval between initial treatment and follow-up imaging. Additional information from MRI reduces the frequency of reoperations to achieve clear margins and reduces the rate of unplanned (salvage) mastectomy subsequent to the initial BCS. This can have cost benefits for patients and the health care system, reduce surgical complications, reduce anxiety, and improve the quality of life of patients. May confirm or rule out the feasibility of nipple-sparing mastectomy. In the setting of Paget disease with negative conventional imaging studies, MRI can identify underlying breast malignancy, facilitating proper treatment planning.	Higher breast biopsy rates, including some lesions that will be negative for cancer (i.e., false-positive by MRI). Higher mastectomy rates with MRI when disease extent is greater than shown on conventional imaging. Repeat (short-interval follow-up) MRIs may be required for BI-RADS 3 lesions if an MRI-guided biopsy was not conducted or with benign breast biopsies. More aggressive surgery or other treatment due to knowledge of additional lesions may not change survival outcomes. MRI is not necessarily more accurate in estimating tumour size than other imaging; the optimal modality may vary with tumour characteristics.
Specificity	Specificity is generally greater than 70%, and up to 97% has been reported [1]. MRI specificity depends on study populations, technical methods, and criteria for interpretation.	Specificity may be lower than mammography in some MRI centres or for some applications. MRI-detected lesions require biopsy for tissue confirmation and may include false-positive lesions.
Patient Factors	May reduce the mastectomy rate in patients initially opting for mastectomy due to fear of more extensive disease and not due to clinical factors. Reduction in anxiety for some patients as they are more confident regarding the appropriateness of treatment planned or received.	Some patients are not suitable for MRI (anxiety, claustrophobia, MRI does not accommodate body habitus or other patient concerns) or do not want to undergo this procedure. Increased anxiety for some patients regarding MRI procedures or biopsies, or while waiting for these to occur or results to be reported.
Adverse Effects		Gadolinium contrast agents may cause allergic reactions (≈0.1% of patients). Gadolinium retention, especially after multiple MRIs, has been reported in the brain; long-term effects are uncertain but have not been reported to date. Accumulation depends on the type of contrast agent and cumulative exposure. Nephrogenic systemic fibrosis may occur in patients with acute kidney injury or severe chronic kidney disease; the risk varies with the type and volume of gadolinium contrast agent used.
Delay in Treatment		Breast MRI use may potentially lead to delays in treatment due to both MRI scheduling and the characterization of any identified lesions (biopsies and histopathology analysis/reporting). May increase anxiety for patients while waiting for treatment.
Equity	Universal access to preoperative MRI would result in more health care equity, provided equivalent facilities and staffing are available.	Breast MRI, including expertise for interpretation, is not available in all centres, and some patients may need to travel long distances.
Cost	Better lesion characterization may reduce operative costs by reducing rates of reoperations (direct surgical costs for multiple operations, treating surgical complications, patient time), costs to treat metachronous contralateral breast cancer, and longer-term costs due to decreased recurrence.	The addition of an MRI and subsequent biopsy of lesions will add to the initial diagnostic cost.

Abbreviations: BCS, breast conserving surgery; BI-RADS, Breast Imaging Reporting and Data System; MRI, magnetic resonance imaging.