BREAKOUT -International Breast Cancer Biomarker, Standard of Care and Real World Outcomes Study BREAKOUT is a prospective cross-sectional cohort study of human epidermal growth factor receptor 2 negative metastatic breast cancer patients who have started 1st line systemic cytotoxic chemotherapy. The study will estimate the prevalence of germline breast cancer susceptibility gene in an otherwise unselected population, describe the treatments administered and estimate the associated clinical outcomes of overall survival and progression-free survival amongst mutation carriers within the context of a low poly ADP ribose polymerase inhibitor treatment setting. Other exploratory analyses may be undertaken to describe somatic breast cancer susceptibility gene and other homologous recombination repair gene mutations.

Background/Rationale: Within the setting of metastatic human epidermal growth factor receptor 2 negative (HER2-ve) breast cancer limited epidemiological data exist on the prevalence of pathogenic mutations of breast cancer susceptibility gene (BRCA) and other homologous recombination repair (HRR) genes. There are also limited data on the treatments and clinical outcomes of patients with such germline and somatic genetic profiles, particularly within this setting. This epidemiologic study will estimate the prevalence of germline breast susceptibility gene (gBRCA) mutations among metastatic HER2-ve patients who have commenced 1st line systemic cytotoxic chemotherapy and, at that time, are considered to have exhausted hormone therapy options (if hormone receptor positive [HR+ve]), per investigator's opinion. Among those patients with a gBRCA gene mutation, treatment patterns and clinical outcomes will be described. This study may also explore the prevalence of somatic BRCA (sBRCA) mutations and other HRR gene mutations among metastatic HER2-ve patients who have commenced 1st line systemic cytotoxic chemotherapy. The treatment patterns and clinical outcomes may be described among those patients with a sBRCA gene mutation and those with other HRR gene mutations.

Inclusion Criteria:

1. Provision of signed, written and dated informed consent.
2. Adult females (according to the age of majority/adulthood as defined by local regulations).
3. Histologically or cytologically confirmed HER2-ve breast cancer with evidence of metastatic disease.
4. Initiated treatment with 1st line systemic cytotoxic chemotherapy (not hormonal therapy) for metastatic breast cancer in the last 90 days and, at that time, are considered to have exhausted hormone therapy options (if HR+ve).

Exclusion Criteria:

1. Previous enrolment in this study.
2. Involvement in the planning and/or conduct of this study (applies to both AstraZeneca staff and/or staff at the study site).
3. Current participation in a clinical study with an investigational oncology product.
4. Previous PARPi therapy, including, but not limited to, participation in a previous clinical study that included PARPi therapy.
5. Current commencement of PARPi treatment.

Centers for primary care of metastatic HER2-ve breast cancer patients