Evaluation of Discordance in Primary Tumor and Lymph Node Response After Neoadjuvant Therapy in Breast Cancer

Primary tumor and lymph node (LN) response discordance may be observed in breast cancer patients receiving neoadjuvant therapy. We quantified the rate of this discordance and identified factors predictive of it. Almost 15% of primary tumors with complete pathologic response had persistently positive LNs. This is concerning, as we may be undertreating a significant portion of patients. Neoadjuvant therapy (NAT) offers a unique opportunity to assess tumor response to systemic agents. However, a discrepancy may exist between the response of the primary tumor and involved nodes. We report on the frequency of response discordance after NAT in breast cancer. All consecutive node-positive patients receiving NAT in our department from 2009 to 2014 were identified. Patient demographics, and radiologic and pathologic features were tabulated. Tumor response was estimated by magnetic resonance imaging of the breast. Lymph node (LN) response was estimated from pathologic treatment response measurements. Statistical analysis was performed. A total of 108 node-positive patients treated with NAT were eligible for inclusion. Median age was 51.73 years (range, 20-87 years). All patients underwent axillary clearance, and 62% underwent mastectomy. A 40% mean reduction in tumor size was observed. Statistically, a positive correlation between tumor and LN response after NAT was observed (Spearman correlation coefficient, r = 0.46, P < .001). Complete pathologic response was observed in 17 patients (15.7%). However, 21 patients experienced complete LN response, with only 81% of these patients (n = 17) experiencing a complete response in tumor also. A complete response was observed in tumor in 20 patients, and this predicted complete nodal response in 85% of cases (n = 17). Fifteen percent of primary tumors with complete pathologic response had persistently positive LNs. A significant discordance exists between the primary tumor and LN response, representing a concern for the lack of response of occult regional or systemic metastases due to potential biologic heterogeneity.