Differential molecular pathways expression in HER2 positive early breast cancer according to hormone receptor status.

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.