Study to Compare Overall Survival in Medicare Patients With Metastatic Breast Cancer Treated With a Medicine Called Palbociclib in Combination With Aromatase Inhibitor and Aromatase Inhibitor by Itself.

Comparative Assessment of Overall Survival in Medicare Patients With HR+/HER2- Metastatic Breast Cancer Treated With Palbociclib in Combination With Aromatase Inhibitor (AI vs. AI Alone)

A retrospective study of de-identified (to preserve patient privacy) patient information from the SEER-Medicare Database to compare overall survival of first line palbociclib + aromatase inhibitor (AI) therapy versus AI therapy alone treatment in women or men aged 65 and older with newly diagnosed hormone receptor positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer (MBC) in the United States

Inclusion Criteria:

• De novo metastatic (stage IV) disease at initial breast cancer diagnosis during 2015-2019
• HR+/HER2- molecular subtype at diagnosis
• Initiated 1L systemic therapy with palbociclib + AI or AI alone

Exclusion Criteria:

• Patients will be excluded if their metastatic breast cancer diagnosis was first recorded in a death certificate or at the time of autopsy.