This study aims to investigate the correlation between immune-related factors in the tumor stroma and pathological complete response (pCR) in patients with early breast cancer treated with neoadjuvant chemotherapy. In addition, the study evaluates the association between immune-related tumor stroma factors and the presence of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in peripheral blood. The study includes serial blood sampling before and after treatment and during follow-up to assess the prognostic value of these biomarkers for disease progression and recurrence.

Neoadjuvant chemotherapy is widely used in patients with early breast cancer to reduce tumor size and improve surgical outcomes. Achieving a pathological complete response (pCR) is associated with improved prognosis; however, reliable predictive biomarkers are still limited. Recent evidence suggests that immune cells in the tumor microenvironment may influence treatment response.

This study evaluates immune-related tumor stroma factors (including tumor-infiltrating lymphocytes and immune marker profiles) in tumor tissue obtained prior to treatment. In parallel, circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) are assessed from peripheral blood samples collected before neoadjuvant chemotherapy, after completion of treatment, and during follow-up.

The primary objective is to determine whether immune-related tumor stroma factors correlate with pCR after neoadjuvant chemotherapy. Secondary objectives include evaluating the association of immune-related factors with the presence of CTCs and ctDNA and assessing their prognostic value for disease progression and recurrence.

Inclusion Criteria:

• Female patients aged 18 years or older.
• Histologically confirmed early breast cancer.
• Candidates for standard neoadjuvant chemotherapy.
• Ability to provide informed consent.

Exclusion Criteria:

• Luminal A subtype of breast cancer.
• Prior systemic therapy for breast cancer.
• Serious comorbid conditions that would preclude study participation.

The study population includes adult patients with histologically confirmed early breast cancer treated at the Institute of Oncology Ljubljana who are candidates for standard-of-care neoadjuvant chemotherapy. Participants are enrolled prospectively and followed through surgery and subsequent follow-up to assess pathological complete response (pCR) and associations with tumor-infiltrating lymphocytes and circulating biomarkers.