Axillary ultrasound for prediction of response to neoadjuvant therapy in the context of surgical strategies to axillary dissection in primary breast cancer: a systematic review of the current literature

Purpose: Data on the optimal treatment strategy for patients undergoing neoadjuvant therapy (NAT) who initially presented with metastatic nodes and convert to node-negative disease (cN+ → ycN0) are limited. Since NAT leads to axillary downstaging in 20–60% of patients, the question arises whether these patients might be offered less-invasive procedures than axillary dissection, such as sentinel node biopsy or targeted removal of lymph nodes marked before therapy. Methods: We performed a systematic review of clinical studies on the use of axillary ultrasound for prediction of response to NAT and ultrasound-guided marking of metastatic nodes for targeted axillary dissection. Results: The sensitivity of ultrasound for prediction of residual node metastasis was higher than that of clinical examination and MRI/PET in most studies; specificity ranged in large trials from 37 to 92%. The diagnostic performance of ultrasound after NAT seems to be associated with tumor subtype: the positive predictive value was highest in luminal, the negative in triple-negative tumors. Several trials evaluated the usefulness of ultrasound for targeted axillary dissection. Before NAT, nodes were most commonly marked using ultrasound-guided clip placement, followed by ultrasound-guided placement of a radioactive seed. After chemotherapy, the clip was detected on ultrasound in 72–83% of patients; a comparison of sonographic visibility of different clips is lacking. Detection rate after radioactive seed placement was ca. 97%. Conclusion: In conclusion, ultrasound improves prediction of axillary response to treatment in comparison to physical examination and serves as a reliable guiding tool for marking of target lymph nodes before the start of treatment. High quality and standardization of the examination is crucial for selection of patients for less-invasive surgery.