Study on patients undergoing surgery for breast cancer. Objective: to characterize the intratumoral microbiota and integrate these findings with clinicopathologic data, the estrobolome, and gut microbiota, with analyses stratified by molecular subtype (Luminal A, Luminal B, HER2-enriched [human epidermal growth factor receptor 2-enriched], and TNBC [triple-negative breast cancer]).

Enrollment: consecutive recruitment in the operating room based on the availability of biopsy/histological material.

Samples: tumor tissue, adjacent normal tissue; urine (for indirect assessment of estrobolome activity); and stool. Strict anti-contamination measures will be implemented.

Exploratory outcomes: differences across subtypes, associations with features of the TME (tumor microenvironment), including TILs (tumor-infiltrating lymphocytes), and markers of progression or treatment resistance

Inclusion Criteria:

• Women ≥18 years with primary, non-metastatic breast cancer (BC) undergoing surgery.
• Availability of sufficient tumor and adjacent normal tissue for research purposes after completion of diagnostic sampling.
• Written informed consent

Exclusion Criteria:

• Active systemic infection or fever >38.0°C within 72 h pre-surgery.
• Antibiotics within 14 days pre-sampling (recorded; analyses adjusted).
• Prior ipsilateral BC surgery for current lesion (except re-excision with fresh tissue).
• Any condition preventing compliance with the study protocol.