This multicountry, multicenter, retrospective, non-interventional study involving patients diagnosed with HER2-positive unresectable or metastatic breast cancer mBC will be conducted to understand the demographic and clinico-pathological profile of the patients, diagnostic practices for human epidermal growth factor receptor 2 (HER2) status, current treatment landscape and sequencing of therapies, associated burden of toxicities with all lines of treatment (LOTs), and survival outcomes in the real-world setting.

The study will involve patients diagnosed with HER2-positive unresectable or mBC since the earlier date between the date of trastuzumab emtansine ([T-DM1] Kadcyla) becoming available through reimbursement or patient access programme as a valid local treatment option or 01 January 2017 and who received at least 1 LOT. The data will be collected from the date of diagnosis of unresectable or mBC (index date) to the end of follow-up (ie, until death, the last medical record entry, or date of data extraction, whichever is earlier). The study will not have any study-specific patient visits or a longitudinal follow-up. All available data will be extracted from patients' medical records or obtained from patients themselves after obtaining an informed consent unless a waiver is granted by the local Institutional Review Board (IRB)/Institutional Ethics Committee (IEC)/Ethics Committee (EC). The informed consent may be obtained at the time of patients routine clinical care visit to the oncology centre. The data on different types of treatment received by the patients, socio-demographics, and clinico-pathological characteristics will be extracted from patients medical records up to the date informed consent was obtained.

This study will be conducted in non-US and non-European countries including Australia, Brazil, Hong Kong, Korea, Singapore and Taiwan. The total number of patients in the study will be approximately a minimum of 570 and a maximum of 830 patients. The study will be implemented at approximately 50 to 100 oncology centres spanning across 6 countries in the AstraZeneca (AZ) International Region (ie, non-US, non-European countries).

Inclusion Criteria:

• Adult female or male patients ≥18 years old or 'adults' according to the age of majority as defined by the local regulations
• Patient or next of kin/legal representative willing and able to provide written informed consent according to the local regulations unless a waiver is granted by the local IRB/IEC/EC
• Patients' medical records showing a diagnosis of HER2-positive unresectable or mBC (can be either de novo advanced disease, progression or recurrence of previous early-stage HER2-positive BC) since the available date of T-DM1 (Kadcyla) through reimbursement or patient access programme as a valid local treatment option or 01 January 2017, whichever is earlier and with the availability of at least 12 months of follow-up data (from the date of diagnosis of unresectable or mBC) in the medical records at the participating site, unless patient died within the first 12 months of diagnosis
• Patients completing at least 1 LOT for HER2-positive unresectable or mBC

Exclusion Criteria:

• Patients with HER2-negative unresectable or mBC at index diagnosis
• Patients with a change in HER2 status from positive to negative at the progression from early-stage to advanced-stage disease (ie, shown on a repeat biopsy at diagnosis of advanced-stage disease) will be excluded (patients who change from HER2-positive to negative on repeat biopsy during treatment for advanced-stage disease may be included)
• Patients with concomitant cancer at the time of diagnosis of HER2-positive unresectable or mBC except for the non-metastatic non-melanoma skin cancers, or in situ, or benign neoplasms; a cancer is considered concomitant if it occurs within 5 years of HER2-positive breast cancer diagnosis
• Patients who at the time of data collection for this study are participating or have participated in an interventional study that remains blinded

Study population will include patients who are diagnosed with HER2-positive unresectable or mBC and have received at least 1 LOT in the advanced setting.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal. All requests will be evaluated as per the AZ disclosure commitment:

https://astrazenecagrouptrials.pharmacm.com /ST/Submission/Disclosure.

Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA Pharma Data Sharing Principles. For details of our timelines, please refer to our disclosure commitment at:

https://astrazenecagrouptrials.pharmacm.com /ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the de-identified individual patient-level data in an approved sponsored tool. Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at:

https://astrazenecagrouptrials.pharmacm.com /ST/Submission/Disclosure.