Breast cancer is the most common cancer in Taiwanese women. Most of them were diagnosed in relatively early stages. Only 700 metastatic breast cancer were registered in Official Cancer Registration 2012, while more than11,305 were registered as early breast cancer. With broadly application of aromatase inhibitors, hormonal-receptor-positive breast cancer patients can survive longer and longer. However, there is no prevalence of metastatic breast cancer can be available yet. NHIA database coverage is more than 90% population in Taiwan, thus it can be an appropriate surrogate of prevalence. In this retrospective database analysis, we will explore the real world experience on aromatase inhibitor use for breast cancer in Taiwan.

Inclusion Criteria:

• hormonal receptor positive, human epidermal growth factor receptor 2 negative breast cancer

Exclusion Criteria:

-

hormonal receptor positive, human epidermal growth factor receptor 2 negative breast cancer

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.