HER2 Gene Amplification in ER-positive HER2 Immunohistochemistry 0 or 1+Breast Cancer With Early Recurrence

Background/Aim: In estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, standard chemotherapies as well as adjuvant endocrine therapy might not be enough for prevention of early relapse. Materials and Methods: We focused on ER-positive, HER2 immunohistochemistry (IHC) 0 or 1+ breast cancer, and retrospectively examined HER2 gene amplification and TP53 mutation in breast cancer tissues in patients with or without early recurrence. Post-relapse survival in patients with early recurrence was also analyzed by mutation status of HER2 and TP53. Results: Surprisingly, amplification of the HER2 gene was found in 15% of patients with early recurrence. None of the patients without relapse had HER2-amplified tumors. Post-relapse survival in patients with HER2 gene amplification and/or TP53 mutation in primary tumors was shorter than that in patients without these mutations, especially among postmenopausal women. Conclusion: HER2 gene amplification exists in ER-positive, HER2 IHC 0 or 1+ breast cancer in patients who developed early distant metastasis.