This is a multicenter, non-interventional, retrospective, real-world study that enrolled patients diagnosed with HER2-positive unresectable or metastatic breast cancer. This study will be conducted to understand the treatment pattern and sequencing of therapies, survival outcomes, and associated burden of toxicities with line of treatment in the real world.

The treatment landscape has changed dramatically with the lack of real-world evidence for usage and the efficacy of newly approved drugs in China. This multicenter, retrospective, non-interventional study will include patients newly diagnosed with HER2-positive unresectable or metastatic breast cancer, or first recurrent from early breast cancer.

The primary objective of this real-world study is to describe the treatment patterns of HER2-positive unresectable or metastatic breast cancer in China. Secondary objectives will include describing the demographic and clinicopathological characteristics of patients, efficacy of different treatment regimens, treatment options and efficacy of brain metastases, and safety and tolerability of different treatment regimens in patients with HER2-positive unresectable or metastatic breast cancer.

Inclusion Criteria:

• Male or female patients ≥ 18 years of age at the time of diagnosis of unresectable or metastatic breast cancer
• Participants with first diagnosis of unresectable or metastatic breast cancer, or first recurrence of HER2-positive breast cancer since January 1, 2020. Participants were eligible if they were HER2-positive in the early operable stage and HER2-negative in the advanced stage. HER2 positive was defined with the reference to the Chinese guidelines for HER2 positive breast cancer at the time of testing
• Participants have received at least one systemic therapy for advanced breast cancer

Exclusion Criteria:

• Participants with concomitant cancer at the time of diagnosis of HER2-positive unresectable or metastatic breast cancer, 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.
• Participants who are/were currently/previously enrolled in a clinical trial and have not been unblinded during the data collection interval of the study
• Participants with critical missing data from their medical records or other patients deemed by the investigator to be ineligible for inclusion

The study population will be participants with a first diagnosis of HER2-positive unresectable or metastatic breast cancer or first recurrence between January 1, 2020 and August 31, 2022, who have at least one record of late systemic therapy, and were followed up until August 31, 2022. The study will be implemented at 4-6 top hospitals in Tier 1/2 cities spanning across China.

Patient data will be retrospectively collected using the electronic medical record and hospital information system or other available resources, including laboratory test results, imaging, pathology reports, medical records, surgical records, prescription diagnoses, inpatient visits and hospitalizations.