This prospective observational study aims to evaluate whether exosomal microRNA profiles derived from tumor tissue and blood serum are associated with pathological complete response (pCR) to neoadjuvant chemotherapy (NAC) in patients with breast cancer.

Breast cancer patients with similar clinical and pathological features may respond differently to treatment, underscoring the need for reliable biomarkers that can help predict therapeutic outcomes. Exosomes are small extracellular vesicles released by tumor cells that carry molecular signals, including microRNAs, which may reflect tumor behavior and treatment sensitivity.

In this study, patients with breast cancer receiving standard NAC as part of routine clinical care will be followed prospectively. Exosomal microRNA profiles obtained from tumor tissue and blood samples collected during routine diagnostic and treatment procedures will be analyzed and compared with pathological complete response (pCR) assessed after completion of neoadjuvant chemotherapy.

A group of patients with benign breast disease will be included as a reference control for comparative analyses.

The results of this study may contribute to the identification of minimally invasive biomarkers that support personalized treatment strategies in breast cancer.

This prospective, multicenter, non-interventional observational study is designed to investigate tissue- and serum-derived exosomal microRNA profiles and their association with pathological complete response (pCR) to neoadjuvant chemotherapy (NAC) in patients with locally advanced breast cancer (LABC).

Although established clinicopathological parameters, including hormone receptor status, Human Epidermal Growth Factor Receptor 2 (HER2) expression, and Ki-67 index, are routinely used to stratify breast cancer subtypes and provide important prognostic and predictive information, inter-patient variability in treatment response remains substantial. These parameters do not fully capture the dynamic biological heterogeneity of tumors or reliably predict individual response to neoadjuvant chemotherapy in all patients. This underscores the need for additional, minimally invasive molecular biomarkers that may complement existing clinicopathological factors and better reflect tumor biology, thereby supporting personalized therapeutic strategies.

Exosomes are small extracellular vesicles released by tumor and stromal cells that carry molecular cargo, including microRNAs, which reflect the biological activity of their cells of origin. Due to their stability and detectability in both tumor tissue and peripheral blood, exosomal microRNAs represent promising candidates for monitoring treatment response and identifying mechanisms of chemotherapy sensitivity or resistance.

In this study, patients with histologically confirmed locally advanced breast cancer who are scheduled to receive standard-of-care neoadjuvant chemotherapy will be prospectively enrolled. The study is strictly observational, and no additional interventions, blood draws, tissue biopsies, or sample collection procedures will be performed for research purposes. Exosomal miRNA analyses will be conducted exclusively on residual serum samples obtained during routine clinical blood tests and leftover tumor tissue collected for diagnostic or surgical purposes as part of standard clinical care.

Exosomal microRNA expression profiles derived from tissue and serum samples will be analyzed using molecular techniques and correlated with pathological complete response (pCR) following completion of neoadjuvant chemotherapy. Pathological response will be evaluated using established tumor regression grading systems, including pathological complete response (pCR) and standardized tumor regression grading criteria.

In addition, residual samples obtained from patients with histologically confirmed benign breast lesions will be included as a reference control group to assess the specificity of molecular alterations observed in malignant disease.

The primary objective of the study is to evaluate whether tissue- and serum-derived exosomal microRNA expression patterns are associated with pathological complete response (pCR) to neoadjuvant chemotherapy. Secondary objectives include comparing tissue- and serum-based exosomal microRNA profiles, exploring associations with clinicopathological variables, and assessing the potential of exosomal microRNAs as predictive biomarkers of treatment sensitivity or resistance.

Inclusion Criteria:

• Female patients aged 18 years or older
• Histologically confirmed locally advanced breast cancer scheduled to receive neoadjuvant chemotherapy
• Availability of residual tumor tissue and/or serum samples obtained during routine clinical care
• Ability to provide written informed consent

Exclusion Criteria:

• Male sex
• Age under 18 years
• Prior systemic chemotherapy or radiotherapy administered for the current breast disease before enrollment.
• Evidence of metastatic disease at diagnosis (for breast cancer cohort)
• Pregnancy or breastfeeding
• Any condition that precludes the availability or adequate quality of tissue or blood samples for research purposes

Female patients aged 18 years or older will be enrolled into two cohorts:

1. patients with histologically confirmed breast cancer who are scheduled to receive neoadjuvant chemotherapy, and
2. patients with histologically confirmed benign breast disease. Participants will be recruited from multiple clinical centers.

Only leftover tumor tissue and serum samples obtained during routine diagnostic or therapeutic procedures will be used for exosomal microRNA analysis.

Individual participant data sharing has not yet been determined. Any future data sharing will be subject to ethical approval, institutional regulations, and applicable data protection laws. De-identified data may be considered for sharing upon reasonable request.