This study is planned as a secondary data use (SDU) study and the data collection will be performed retrospectively. Patients who presented to the participating sites with metastatic breast cancer will be defined, and patients' data will be recorded into a database.

This study is planned as a secondary data use (SDU) study and the data collection will be performed retrospectively. Patients who presented to the participating sites with metastatic breast cancer will be defined and patients' data will be recorded into a database. The study will be performed at clinical centers located in the populated cities with high clinical and diagnostic standards including patients presented with metastatic disease will be recorded. It is also planned to collect data on the treatment of metastatic breast cancer in line with institutional guidelines at academic and private centers which has implemented high quality clinical and pathologic standards.

This retrospective study is designed to record, define and evaluate the changes in the presentation patterns, pathological subtypes and outcomes of metastatic breast cancer patients in relation with the evolution of overall and progression-free survival rates following the changes in treatment approaches over the last decade based on the evolving/different treatment regimens of metastatic breast cancer.

These findings will shed light on how changes in metastatic patterns have influenced practice patterns, as well as the generalizability of this data to the current knowledge and physician's adherence to adopt contemporary treatment options which have been integrated within standard treatment algorithms.

Demographic characteristics of metastatic breast cancer patients, diagnosis of disease and treatments initiated for all patients receiving first line (1L) and second line (2L) treatment who were admitted to the clinical centers starting from year 2010 will be retrospectively collected for this study. Data of patients who previously consented for institutional data sharing will be retrieved from patient charts and recorded in a secure electronic registry.

The study data will be categorized on two different patient characteristics: Metastatic pattern at presentation [recurrent metastatic breast cancer (rMBC) or de-novo metastatic breast cancer (dnMBC)] of patient and date of initial presentation for diagnosis and treatment. The study is planning to analyze patients with follow-up data of minimum 3 years and the data recording will eventually plan to construct two cohorts based on the initial diagnosis date; patient diagnosed during Jan 2010-Dec 2014 and Jan 2015-Dec 2019.

The main goal of the study is to define whether if any changes in the treatment practices occurred during the period of data record in line changes occurred with the availability of novel diagnostic methods and treatments for metastatic breast cancer.

Inclusion Criteria:

• Age ≥ 18 years, no upper age limit.
• Must have a definite diagnosis of metastatic breast cancer at the time of initial application at any of the participating clinical centers.
• Patients who were initiated their first treatment at the center where the initial mBC diagnosis was made and whose follow-up and treatment period have continued at the current center.
• Patients must have signed an informed consent that allow collection of personal data and protection of patient confidentiality according to the standard procedures of each participating center.

Exclusion Criteria:

• Patients who were referred to the participating centers for further treatment for a second opinion.

Patients diagnosed with metastatic breast cancer during January 2010-December 2014 and January 2015-December 2019 who were previously treated at the selected/participating clinical centers.