The purpose of this real-world study is to understand the use of palbociclib as first treatment for Hormone receptor positive (HR+) and Human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer in Canada (PALCAN).

The real-world study is not a research study. It involves real patients who receive medicines prescribed by their doctors in the real world. Metastatic breast cancer is the type which has spread from breast to other organs.

HR positive stands for Hormone-receptor cells that have a protein on their surface that binds to one of 2 types of hormones. They are estrogen or progesterone. Both these hormones help cancer cells grow.

HER2 negative describes cells that have a small amount or none of a protein called HER2 on their surface. In normal cells, HER2 helps control cell growth. Cancer cells that are HER2 negative may grow more slowly and are less likely to come back or spread to other parts of the body.

This study will mainly measure:

- duration of treatment (from start of treatment till end of treatment) among a group of patients taking palbociclib (Ibrance) in combination with hormone therapy as first line treatment for HR+ HER2- metastatic breast cancer.

Inclusion Criteria:

• Received at least one cycle of palbociclib as first line therapy for metastatic breast cancer between 01 January 2016 and 31 December 2022
• Histologically confirmed HR+/HER2- metastatic breast cancer
• Minimum of 3 months available follow-up on palbociclib

Exclusion Criteria:

• Received a different CDK4/6 inhibitor before palbociclib in the first line
• Received other systemic therapy, including hormone therapy, 15-60 days prior to initiation of palbociclib
• Invalid or incomplete records (more specifically, complete duration of treatment on palbociclib, endocrine therapy or LHRH)
• Death date recorded on or before the date of index date

Treatment of Canadian women patients on palbociclib with HR+/HER2- metastatic 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.