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Purpose: Hormone receptors (HR) status in HER2 + breast cancer (BC) is a recognized stratification factor with relevant clinical implication. According to HR expression, HER2 + BC show different clinical characteristics, treatment sensitivity and prognosis. The interaction between HR and HER2 pathways remains incompletely understood. Methods: Thirty-four HER2 + BC were included: 18 tumors with HER2+/HR + and 16 with HER2+/HR−. The expression of 770 genes and 13 molecular pathways were evaluated using Nanostring PanCancer Pathway panel performed on FFPE BC biopsies. Results: Gene expression analysis identified 127 genes with significantly different expression between the two cohorts. 83% of these genes were overexpressed in HER2+/HR− cohort. Globally, 23% of them belonged to PI3K pathway (41 genes), 15% to Trascriptional regulation (26 genes) and 12% to MAPK (22 genes). Regarding pathway expression, PI3K, MAPK and NOTCH were significantly differently expressed between the two groups (p = 0.003, p = 0.0018 and p = 0.02, respectively), all of them were overexpressed in HER2+/HR− tumors. Conclusions: According to HR status, HER2 + tumors express different pathways profiles: the overexpression of PI3K, MAPK and NOTCH pathways in HER2+/HR− group could justify different survival outcomes and treatment sensitivity. The identification of tumor driver pathways may be a useful instrument for individualized pathway-directed therapies. Further clinical implications are warranted. [ABSTRACT FROM AUTHOR]

Simple Summary: Breast cancer is a leading cause of female cancer-related death worldwide. Anti-HER2-targeted therapies dramatically improved prognosis for HER2-positive breast cancer patients. Despite that, growing drug resistance due to the pressure of therapy is relatively frequent. For that reason, it is necessary to find biomarkers able to predict treatment sensitivity and survival outcomes. Increasing research has shown how miRNAs, secreted by tumor cells, are strongly involved in cancer development. In this review, we will discuss the recent evidence on the predictive and prognostic value of miRNAs involved in HER2-positive early breast cancer progression. MicroRNAs (miRNA) are small noncoding RNAs that can act as both oncogene and tumor suppressors. Deregulated miRNA expression has been detected in human cancers, including breast cancer (BC). Considering their important roles in tumorigenesis, miRNAs have been investigated as potential prognostic and diagnostic biomarkers. Neoadjuvant setting is an optimal model to investigate in vivo the mechanism of treatment resistance. In the management of human epidermal growth factor receptor-2 (HER2)-positive early BC, the anti-HER2-targeted therapies have drastically changed the survival outcomes. Despite this, growing drug resistance due to the pressure of therapy is relatively frequent. In the present review, we focused on the main miRNAs involved in HER2-positive BC tumorigenesis and discussed the recent evidence on their predictive and prognostic value. [ABSTRACT FROM AUTHOR]