There is substantial evidence to support the routine use of contrast-enhanced MRI to stage, monitor early response, and assess for residual and recurrent disease given the overall high sensitivity and relatively high specificity of this technique [1]. Dynamic contrast-enhanced MRI is a sensitive tool to determine extent of disease in the breast, especially in young patients (<50 years of age), with sensitivity approaching 90% and specificity ranging between 50% and 97% [1,32]. To accurately evaluate for response to NAC, a pretreatment MRI must be obtained to serve as a baseline for comparison. MRI is particularly useful in the assessment of multifocal and multicentric disease, which is often underestimated on both mammography and US [28]. In fact, multifocal and multicentric disease are detected in up to 16% of patients on staging MRI according to a study by Houssami et al [33]. A prospective study of 216 patients demonstrated that size determination on MRI was superior to clinical examination in predicting pathologic response both before, during, and after completion of NAC [31]. The enhancement pattern on the pretreatment MRI also indicates how reliable this technique will be in evaluating response. Nonmass enhancement on the pretreatment MRI has been shown to reveal a scattered cell pattern more commonly on posttreatment imaging, thereby making assessment of residual disease more difficult [34]. However, when a mass with well-defined margins is seen, MRI can more accurately predict the amount of residual disease on posttreatment imaging [34]. In addition, several studies have shown that MRI is more accurate than mammography and US in defining disease extent for invasive lobular cancer [32,35,36]. MRI can reliably assess the chest wall because pectoral or intercostal muscle enhancement correlates well with invasion [37].
Monitoring Response to Neoadjuvant Systemic Therapy for Breast Cancer. There is substantial evidence to support the routine use of contrast-enhanced MRI to stage, monitor early response, and assess for residual and recurrent disease given the overall high sensitivity and relatively high specificity of this technique [1]. Dynamic contrast-enhanced MRI is a sensitive tool to determine extent of disease in the breast, especially in young patients (<50 years of age), with sensitivity approaching 90% and specificity ranging between 50% and 97% [1,32]. To accurately evaluate for response to NAC, a pretreatment MRI must be obtained to serve as a baseline for comparison. MRI is particularly useful in the assessment of multifocal and multicentric disease, which is often underestimated on both mammography and US [28]. In fact, multifocal and multicentric disease are detected in up to 16% of patients on staging MRI according to a study by Houssami et al [33]. A prospective study of 216 patients demonstrated that size determination on MRI was superior to clinical examination in predicting pathologic response both before, during, and after completion of NAC [31]. The enhancement pattern on the pretreatment MRI also indicates how reliable this technique will be in evaluating response. Nonmass enhancement on the pretreatment MRI has been shown to reveal a scattered cell pattern more commonly on posttreatment imaging, thereby making assessment of residual disease more difficult [34]. However, when a mass with well-defined margins is seen, MRI can more accurately predict the amount of residual disease on posttreatment imaging [34]. In addition, several studies have shown that MRI is more accurate than mammography and US in defining disease extent for invasive lobular cancer [32,35,36]. MRI can reliably assess the chest wall because pectoral or intercostal muscle enhancement correlates well with invasion [37].