Factors influencing HER2 discordance in nonmetastatic breast cancer and the role of neoadjuvant therapy.

Objective: The rates of and the factors influencing HER2 discordance in patients receiving neoadjuvant therapy for breast cancer are investigated. Methods: This study retrospectively examines the rates of HER2 and hormone receptor discordance between the biopsy and postoperative resection specimens of 400 female early-stage breast cancer patients. Results: 133 (33.3%) patients had received neoadjuvant therapy. The rate of HER2 discordance between biopsy and resection specimens was 1.7% in the control group and 5.3% in the neoadjuvant therapy group (p = 0.018). The rate of HER2 discordance was higher in younger patients and in patients with T1 tumors in the neoadjuvant therapy group. Conclusion: Neoadjuvant therapy, age <40 years and smaller tumor size were independent risk factors for HER2 discordance.