Quantitative Assessment of the Echogenicity of a Breast Tumor Predicts the Response to Neoadjuvant Chemotherapy

SIMPLE SUMMARY: B-mode US is a widely available, inexpensive, and non-invasive technique. This method is used in monitoring the neoadjuvant chemotherapy (NAC) in breast cancer (BC). In the presented study we combined the result from B-mode ultrasound examination with quantitative information about the characteristics and structure of the tissue in predicting the response to neoadjuvant chemotherapy in BC patients. We used echogenicity (ΔEcho) as B-mode features and the Kullback-Leibler divergence (ΔKLD) method as a quantitative parameter to provide information on changes in image echogenicity, to determine differences between the distributions of the ultrasound echo amplitude from tumor during NAC. The ΔKLD parameter alone is an accurate predictor of response to treatment after the second course of therapy (cut-off ≥70%, AUC = 0.85). Combining both parameters (ΔKLD and ΔEcho) led to an increase in sensitivity without significant deterioration of other statistical parameters and allowed to accurately predict non-responding tumors. ABSTRACT: The aim of the study was to improve monitoring the treatment response in breast cancer patients undergoing neoadjuvant chemotherapy (NAC). The IRB approved this prospective study. Ultrasound examinations were performed prior to treatment and 7 days after four consecutive NAC cycles. Residual malignant cell (RMC) measurement at surgery was the standard of reference. Alteration in B-mode ultrasound (tumor echogenicity and volume) and the Kullback-Leibler divergence (kld), as a quantitative measure of amplitude difference, were used. Correlations of these parameters with RMC were assessed and Receiver Operating Characteristic curve (ROC) analysis was performed. Thirty-nine patients (mean age 57 y.) with 50 tumors were included. There was a significant correlation between RMC and changes in quantitative parameters (KLD) after the second, third and fourth course of NAC, and alteration in echogenicity after the third and fourth course. Multivariate analysis of the echogenicity and KLD after the third NAC course revealed a sensitivity of 91%, specificity of 92%, PPV = 77%, NPV = 97%, accuracy = 91%, and AUC of 0.92 for non-responding tumors (RMC ≥ 70%). In conclusion, monitoring the echogenicity and KLD parameters made it possible to accurately predict the treatment response from the second course of NAC.