Treatment Patterns and Clinical Outcomes Among Patients With HR+/HER2- mBC Receiving Palbociclib Combination Therapy in the US Community Oncology Setting.

• Cohort 1a (Pb-AI)
  Patients who initiated treatment with an aromatase inhibitor (letrozole, exemestane, or anastrozole) palbociclib combination therapy as first-line treatment in the advanced or metastatic setting.
• Cohort 1b (Pb-FUL)
  Patients who initiated palbociclib-fulvestrant combination therapy as first-line or beyond therapy in the advanced or metastatic setting.
• Cohort 2a (AI mono)
  Patients who initiated treatment with an aromatase inhibitor (letrozole, exemestane, or anastrozole) as a monotherapy as first-line treatment in the advanced or metastatic setting.
• Cohort 2b (FUL mono)
  Patients who received fulvestrant monotherapy as first-line or beyond therapy in the advanced or metastatic setting.

Inclusion Criteria:

1. Patients with a documented diagnosis of hormone receptor-positive (estrogen receptor-positive or progesterone receptor-positive), human epidermal growth factor receptor 2-negative mBC.
2. Aged 18 years at initial recorded diagnosis of mBC.

3. Initiated one of the following qualifying regimens within the USON during the study identification period:

   1. Palbociclib combination therapy with an aromatase inhibitor (letrozole, exemestane, or anastrozole) among patients as first-line therapy in the advanced or metastatic setting;
   2. Palbociclib combination therapy with fulvestrant following as first-line or beyond therapy in the advanced or metastatic setting;
   3. Aromatase inhibitor (letrozole, exemestane or anastrozole) monotherapy as first-line treatment in the advanced or metastatic setting;
   4. Fulvestrant monotherapy as first-line or beyond therapy in the advanced or metastatic setting.
4. Received care at a USON site(s) utilizing the full EHR capacities of iKM at the time of treatment.
5. EHR data available from the USON site(s) where the patient received treatment are accessible for research purposes.
6. During the study observation period, patients observed with at least 2 visits after the index date.

Exclusion Criteria:

1. Enrollment in an interventional clinical trial during the study observation period since clinical trial participants may have clinical scenarios that deviate from the population of interest.
2. Among the Pb-AI and AI mono cohorts, evidence of prior treatment with other CDK 4/6 inhibitors (ribociclib or abemaciclib), aromatase inhibitors (letrozole, exemestane, or anastrozole), tamoxifen, raloxifene, toremifene, or fulvestrant in the advanced or metastatic setting.
3. Among the Pb-FUL and FUL mono cohorts, evidence of prior treatment with CDK 4/6 inhibitors (ribociclib or abemaciclib) in the advanced or metastatic setting.
4. Receipt of treatment indicated for another primary cancer during the study observation period or history of another primary cancer within the USON iKM EHR database.