MRI of the axilla is only 38% to 61% sensitive for detection of residual disease after NAC [112,113]; therefore, surgical sampling is the standard of care [114,120-122]. In a retrospective study of 135 clinically node-positive patients after NAC, MRI had a low negative predictive value (NPV) of 26% for predicting axillary disease when a positive MRI was defined by node >1 cm, cortex >3 mm, loss of hilum, or irregular contour [121]. In a retrospective study of 269 node-positive patients, posttreatment MRI was only 38% sensitive, 76% specific, and 58% accurate in predicting the pathology of the sentinel lymph node (SLN). In a prospective study of 45 patients, 35 of whom were node-positive, there was no association between posttreatment axillary MRI and surgical pathology; MRI had a high false negative rate (46%), low sensitivity (55%), and specificity (63%) [114]. MRI Breast Without IV Contrast There is no relevant literature to support the use of MRI breast without IV contrast in initial imaging of the axilla after NAC. US Axilla US is not typically performed for initial evaluation of the axilla after initiation of NAC, and the current literature does not specifically evaluate this scenario. The literature on posttreatment axillary US predicting residual nodal disease evaluates patients with established node-positive disease before therapy, as described below. These data cannot necessarily be extrapolated to initial imaging after therapy in the absence of pretreatment axillary evaluation. No imaging test can reliably detect residual nodal disease after NAC, and therefore surgical sampling is the standard of care. In established node-positive patients after therapy, axillary US only demonstrates moderate sensitivity (53%-86%) and specificity (78%) for detecting residual disease with an NPV ranging from 46% to 90% [112,123,124]. Therefore, surgical sampling of axillary lymph nodes after therapy remains the standard of care.
Monitoring Response to Neoadjuvant Systemic Therapy for Breast Cancer. MRI of the axilla is only 38% to 61% sensitive for detection of residual disease after NAC [112,113]; therefore, surgical sampling is the standard of care [114,120-122]. In a retrospective study of 135 clinically node-positive patients after NAC, MRI had a low negative predictive value (NPV) of 26% for predicting axillary disease when a positive MRI was defined by node >1 cm, cortex >3 mm, loss of hilum, or irregular contour [121]. In a retrospective study of 269 node-positive patients, posttreatment MRI was only 38% sensitive, 76% specific, and 58% accurate in predicting the pathology of the sentinel lymph node (SLN). In a prospective study of 45 patients, 35 of whom were node-positive, there was no association between posttreatment axillary MRI and surgical pathology; MRI had a high false negative rate (46%), low sensitivity (55%), and specificity (63%) [114]. MRI Breast Without IV Contrast There is no relevant literature to support the use of MRI breast without IV contrast in initial imaging of the axilla after NAC. US Axilla US is not typically performed for initial evaluation of the axilla after initiation of NAC, and the current literature does not specifically evaluate this scenario. The literature on posttreatment axillary US predicting residual nodal disease evaluates patients with established node-positive disease before therapy, as described below. These data cannot necessarily be extrapolated to initial imaging after therapy in the absence of pretreatment axillary evaluation. No imaging test can reliably detect residual nodal disease after NAC, and therefore surgical sampling is the standard of care. In established node-positive patients after therapy, axillary US only demonstrates moderate sensitivity (53%-86%) and specificity (78%) for detecting residual disease with an NPV ranging from 46% to 90% [112,123,124]. Therefore, surgical sampling of axillary lymph nodes after therapy remains the standard of care.