PT - JOURNAL ARTICLE AU - HIROKO YAMASHITA AU - NAOKO ISHIDA AU - YUTAKA HATANAKA AU - KANAKO HAGIO AU - TOMOHIRO OSHINO AU - TAKASHI TAKESHITA AU - HIROMI KANNO-OKADA AU - AI SHIMIZU AU - KANAKO C. HATANAKA AU - YOSHIHIRO MATSUNO TI - <em>HER2</em> Gene Amplification in ER-positive HER2 Immunohistochemistry 0 or 1+ Breast Cancer With Early Recurrence AID - 10.21873/anticanres.13994 DP - 2020 Feb 01 TA - Anticancer Research PG - 645--652 VI - 40 IP - 2 4099 - http://ar.iiarjournals.org/content/40/2/645.short 4100 - http://ar.iiarjournals.org/content/40/2/645.full SO - Anticancer Res2020 Feb 01; 40 AB - 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.