The purpose of this study is to identify the risk factors of bone metastasis in breast cancer patients so as to develop a dynamic prediction model using real world clinical data. The multicenter data will be retrospectively collected, and the clinical characteristics related to bone metastasis will be analyzed.

Breast cancer is the most common malignant tumor in women worldwide and bones are the most common sites of metastases in breast cancer patients(~70%). Bone metastasis often leads to skeletal-related events (SREs) ,which may not only reduce the quality of life in patients, but also affect the long-term survival. Therefore, early detection and early intervention of bone metastasis are particularly important for breast cancer patients.

Inclusion Criteria:

1. Patients diagnosed with breast cancer by histopathology;
2. Age between 20 and 70 years old;
3. The first diagnosis time is between 2010 and 2020;
4. Complete diagnosis and treatment information, including basic information, breast cancer diagnosis, surgery, recurrence diagnosis data (including the diagnosis of the metastasis sites), anti-tumor treatment data, bone health and bone metastasis-related diagnosis and treatment data, etc.;
5. Sufficient available follow-up information.

Exclusion Criteria:

1. Missing important basic information (including initial and recurrent pathology, stage, pathological grade and time, surgery time, and drug treatment);
2. With distant metastasis at the initial diagnosis;
3. Patients with autoimmune diseases or aggressive viral infections (such as HIV or hepatitis);
4. Other malignant tumors;
5. Unclear information about distant metastasis.

3500 breast cancer patients diagnosed between 2010 and 2020.