ON-treatment Single-cell Analysis for the Identification of Early Tumor Response Biomarkers on Prospective Collected Serial Tumor Biopsies in Triple Negative Breast Cancer Patient During Standard Neoadjuvant Chemo-immunotherapy

Inclusion Criteria:

1. Female patients aged ≥18 years.
2. ECOG performance status 0-1.
3. Histologically confirmed early breast cancer with one of the following molecular profiles:

   * TNBC: ER and PR negative (IHC \<10%) and HER2 negative (IHC 0-1+ or FISH non-amplified).
   * High-risk luminal (ER+/HER2-): ER positive (IHC ≥10%) HER2 negative (IHC 0-1+ or FISH non-amplified), with high-risk features (e.g., Grade 3, PR-negative, high proliferation, high TILS).
4. Clinical indication for neoadjuvant treatment according to standard practice:

   * TNBC: cT1c and/or cN positive, or cT2 (\>2 cm) and/or cN positive (stage II,III).
   * High-risk luminal: features as defined above (Grade 3, PR-negative, high proliferation, ER low).
5. Ability to understand and sign written informed consent for participation in the study, approved by the local Ethics Committee.

Exclusion Criteria:

1. HER2-positive tumors.
2. Multifocal tumors - exclusion if a single index lesion cannot be identified and sampled; otherwise allowed if a representative lesion can be biopsied.
3. Known metastatic disease. 4 Clinical contraindications to the planned neoadjuvant therapy.

5\. Decision for upfront surgery as determined by the multidisciplinary team. 6. Inability to provide informed consent. 7. Pregnancy or breastfeeding. 8. Prior systemic therapy (chemotherapy, immunotherapy, or endocrine therapy) for the current breast cancer before baseline biopsy 9. On-treatment biopsy clinically not feasible or controindicated