Multiple studies show that dynamic contrast-enhanced MRI is the optimal imaging tool to determine disease response, with sensitivity approaching 90%, specificity ranging from 60 to 100%, and an accuracy of approximately 91% [31,32,35,36,43,63-66]. MRI is particularly helpful in patients with documented multifocal and multicentric tumors on the pretreatment study, despite the fact that MRI underestimates disease extent in up to 18% of cases [67,68]. However, there is a lack of consensus in the literature on the optimal imaging interval to assess response to therapy. Tumor measurements on MRI more accurately predict residual tumor and pathologic response than clinical assessment, a finding corroborated in several studies [69-71], with volume measurements performing better than tumor diameter early in treatment after the first cycle of chemotherapy [31]. In a prospective clinical trial of 138 patients, longest diameter on posttreatment MRI was superior to both mammography and clinical breast examination in detecting residual disease. MRI tumor volume was also shown to predict recurrence free survival in a trial of 162 patients [72]. The ability of MRI to evaluate disease response is variable on the basis of tumor subtype, being more effective for invasive lobular carcinoma, triple-negative, and HER2/neu-positive tumors and less accurate for luminal subtypes (ER and/or progesterone receptor positive, HER2/neu-positive or negative), with an overall accuracy of approximately 75% [73-81]. A study of 208 patients suggested that patients who can safely consider breast conservation therapy after NAC have tumors <3 cm in maximal size on pretreatment MRI, reduction in tumor size on posttreatment MRI, and more often have HER2/neu-positive or triple-negative tumors [67,82]. When the tumor presents as diffuse nonmass enhancement on the pretreatment MRI or is of low nuclear grade, MRI is less helpful in assessing response to therapy [83].
Monitoring Response to Neoadjuvant Systemic Therapy for Breast Cancer. Multiple studies show that dynamic contrast-enhanced MRI is the optimal imaging tool to determine disease response, with sensitivity approaching 90%, specificity ranging from 60 to 100%, and an accuracy of approximately 91% [31,32,35,36,43,63-66]. MRI is particularly helpful in patients with documented multifocal and multicentric tumors on the pretreatment study, despite the fact that MRI underestimates disease extent in up to 18% of cases [67,68]. However, there is a lack of consensus in the literature on the optimal imaging interval to assess response to therapy. Tumor measurements on MRI more accurately predict residual tumor and pathologic response than clinical assessment, a finding corroborated in several studies [69-71], with volume measurements performing better than tumor diameter early in treatment after the first cycle of chemotherapy [31]. In a prospective clinical trial of 138 patients, longest diameter on posttreatment MRI was superior to both mammography and clinical breast examination in detecting residual disease. MRI tumor volume was also shown to predict recurrence free survival in a trial of 162 patients [72]. The ability of MRI to evaluate disease response is variable on the basis of tumor subtype, being more effective for invasive lobular carcinoma, triple-negative, and HER2/neu-positive tumors and less accurate for luminal subtypes (ER and/or progesterone receptor positive, HER2/neu-positive or negative), with an overall accuracy of approximately 75% [73-81]. A study of 208 patients suggested that patients who can safely consider breast conservation therapy after NAC have tumors <3 cm in maximal size on pretreatment MRI, reduction in tumor size on posttreatment MRI, and more often have HER2/neu-positive or triple-negative tumors [67,82]. When the tumor presents as diffuse nonmass enhancement on the pretreatment MRI or is of low nuclear grade, MRI is less helpful in assessing response to therapy [83].