This study is an observational study being carried out in several hospitals. No extra tests or procedures are required beyond those already part of normal medical care.

The study is sponsored by the University of Modena and Reggio Emilia and aims to include about 100 patients.

The main goal of the study is to better understand the different biological types of breast cancer in patients who have hormone receptor-positive (HR-positive), HER2-negative breast cancer related to BRCA gene mutations. In particular, the study will explore whether these cancers tend to belong to molecular types that may respond less to endocrine or CDK4/6 inhibitor therapy.

The study also compares cancers linked to BRCA1 and BRCA2 mutations and investigates whether the different biological types are associated with differences in disease outcomes and response to treatment.

Inclusion Criteria:

• Age 18 years or older
• Patients carrying a pathogenic or likely pathogenic germline variant in BRCA1 or BRCA2 with a histologically confirmed diagnosis of HR+/HER2-negative breast cancer
• Patients with available hospital and/or outpatient medical records for clinical data collection
• Presence of available formally fixed paraffin-embedded (FFPE) breast tumor tissue (primary or metastatic site)

Exclusion Criteria:

• None

Each enrolling center will be responsible for identifying patients eligible for the study. Information will be collected for each patient regarding:

• Patient and treatment characteristics: age, date of diagnosis, and data relating to any treatments received.
• Biological characteristics of the primary disease: histotype, grade, hormone receptor and HER2 expression, and cytoproliferative activity.

The data collected reflect those normally collected in clinical practice for patients diagnosed with breast cancer. No additional specific visits or assessments are required.