Development and validation of an integrated testing strategy for simultaneous detection of ESR-1 and gBRCA mutations via liquid biopsy in HR+/HER2- metastatic breast cancer (mBC) patients, and the creation of a digital gene library to support an evidence-based diagnostic algorithm

Breast cancer is the most prevalent type of tumor and the primary cause of cancer-related deaths among women globally (1). Approximately two-thirds of these tumors express hormone receptors (HR) and lack HER2 overexpression and/or amplification (2). Throughout treatment, resistance frequently develops, with underlying mechanisms that remain largely undefined (3).

Inclusion Criteria:

• Participants must have a confirmed diagnosis of estrogen receptor-positive (ER+) and/or progesterone receptor-positive (PgR+) breast cancer through histological and/or cytological examination by the local laboratory Participants must exhibit HER2-negative breast cancer

  1. or 2+). If IHC is 2+, a negative in situ hybridization (Fluorescent in situ hybridization (FISH), Chromogenic in situ hybridization (CISH), or Silver-enhanced in situ hybridization (SISH)) test is required by local laboratory testing.

     • Participants should be in an advanced or metastatic setting including both those prior to the initiation of treatment for metastatic disease and those who experienced progression following treatment with cyclin-dependent kinases (CDK)4/6 inhibitors. However, the primary tumor should be treated according to the standard of care.
     • Written informed consent must be signed and dated by the patient and the investigator prior to inclusion.

Exclusion Criteria:

• Unable to provide written informed consent

Eligible patients will be identified and enrolled in the study.

• Blood sample collection and plasma purification Blood samples will be collected, and plasma will be purified following biobank procedures.
• ESR1 and gBRCA liquid biopsy-based testing