In search for new targets: Differences of HER2 receptor expression between CNB and synchronous axillary lymph node metastases in 205 patients.

person Laura Weydandt University of Leipzig Medical Center, Department of Gynecology, Leipzig, Germany info_outline Laura Weydandt, Senol Dogan, Ivonne Nel, Lars-Christian Horn, Bahriye Aktas

Authors person Laura Weydandt University of Leipzig Medical Center, Department of Gynecology, Leipzig, Germany info_outline Laura Weydandt, Senol Dogan, Ivonne Nel, Lars-Christian Horn, Bahriye Aktas Organizations University of Leipzig Medical Center, Department of Gynecology, Leipzig, Germany, University of Leipzig, Division of Breast, Gynecologic and Perinatal Pathology, Leipzig, Germany Abstract Disclosures Research Funding No funding received None. Background: Lately large clinical trials have provided new treatment options for patients with metastatic HER2-low breast cancer. Studies have shown that there may be change in the expression of HER2 during disease progression. Yet, it is rarely considered that there can be already differences between primary tumor and synchronous lymph node metastases (LMN) in the primary setting. The aim of the present study was to analyze different HER2 expression profiles between primary tumor and synchronous LNM. Methods: We included 205 patients with primary breast cancer and LNM who underwent oncologic surgery between 2008 and 2021. Formalin-fixed and paraffin-embedded (FFPE) material were routinely examined immunohistochemically according to the ASCO guidelines. Membranous HER2-staining was scored as follows: zero = 0, low = 1+, equivocal = 2+ and positive = 3+. Results: 205 patients were either HER2 low or HER2 zero in CNB. When comparing CNB and LNM 5 (2,4%) patients were HER2 zero in CNB and HER2 low in LNM. 161 (78.5%) patients were HER2 zero in both CNB and LNM. 21 (10.2%) patients had a shift from HER2 low to HER2 zero in LNM. 18 (8,8%) patients had a HER2 low expression in CNB and HER2 zero expression in LNM. Conclusions: There seems to be a high frequency of HER2 heterogeneity between primary tumor and LNM in the primary setting. Different HER2 expression profiles should be considered for an optimal and individual treatment.