Pathologic changes in breast cancer following neoadjuvant chemotherapy: implications for the assessment of response

Neoadjuvant chemotherapy (also known as preoperative or primary chemotherapy) is the treatment of choice for patients with locally advanced breast cancer. One of the main advantages of neoadjuvant chemotherapy is that it allows for assessment of pathologic response to treatment. Clinical and radiologic evaluations of response to neoadjuvant chemotherapy are based on change in tumor size, and the correlation with pathologic response is often inaccurate. Pathologic evaluation of tumor size remains the gold standard for evaluation of residual tumor after chemotherapy. Chemotherapy-induced histomorphologic change is commonly observed in posttreatment resection specimens and can contribute to the less-than-perfect correlation between the clinical assessment of tumor size and the pathologic measurement. Therefore, accurate histologic mapping to the macroscopic and radiologic appearance of the tumor bed is necessary. Cytopathologic changes are also common in residual cancer cells after neoadjuvant chemotherapy and have uncertain clinical relevance. There is a role for the development of new histologic approaches to augment the pathologic and clinical assessment and provide information on the differential response, particularly for tumors in which less than pathologic complete response is achieved.