Identifying predictors of treatment response and molecular changes induced by neoadjuvant chemotherapy and endocrine therapy in hormone receptor-positive/HER2-negative breast cancer: the NEOENDO translational study

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Predictors of response to neoadjuvant chemotherapy (NACT) and endocrine therapy (NET) in hormone receptor-positive (HoR+)/human epidermal growth factor receptor 2 (HER2)-negative breast cancer (BC) are required. Also, pathological and molecular changes induced by both strategies and their impact on patients' outcomes have not been reported so far. In a cohort of 186 patients with early-stage HoR+/HER2-negative BC treated with NACT or NET, we assessed the association of baseline main clinicopathological features and PAM50 gene expression (GE), intrinsic subtypes (IS) and risk-of-relapse (ROR-P) score with pathological outcomes according to treatment strategy. Molecular NACT/NET-induced changes were described and compared, along with their associations with event-free survival (EFS). Comparison of the two cohorts after propensity score matching (PSM) was used as sensitivity analysis. Molecular changes were confirmed in cell lines. NACT was associated with higher rates of residual cancer burden (RCB)-0/I than NET in the overall population (38.2% versus 13.5%, P < 0.001) and after PSM (P= 0.036). PAM50 non-luminal IS were the only independent and positive predictor of RCB-0/I (P= 0.024) in the NACT cohort, while MMP11 messenger RNA levels were the only independent and negative predictor (P= 0.014) in the NET cohort. Both treatments shifted the tumor types toward less aggressive forms (i.e. PAM50 luminal A/normal-like), lowered the risk of recurrence in terms of ROR-P, up-regulated selected immune genes and PAM50 basal-like-related genes/signature and significantly downregulated proliferation-/luminal-/HER2-related genes/signatures, though NACT more than NET. Molecular findings were confirmed after PSM. A net reduction in proliferation-related genes and ROR-P was confirmed in cell lines with chemotherapy and endocrine therapy. Different baseline molecular features associated with diverse kind of responses (ROR-P downstaging, Ki67 reduction or pathological responses) with NACT and NET. Decreasing ROR-P and transitioning the tumor subtype to resemble normal tissue (i.e. PAM50 normal-like) suggested improved EFS. NACT was more effective in the molecular and dimensional tumor 'downstaging' than NET but baseline molecular features associated with differential responses according to treatment strategy. Examining baseline and post-treatment GE might help tailor more personalized and effective care.