This study will evaluate the effect of adding abemaciclib to fulvestrant for the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer that progressed or recurred after previous treatment with a type of drug known as a CDK4/6 inhibitor and endocrine therapy. Participation could last up to 5 years, depending on how you and your tumor respond.

Inclusion Criteria:

• Have a diagnosis of HR+, HER2- locally advanced or metastatic breast cancer

• Have radiologic evidence of disease progression or recurrence either

  • On treatment with a CDK4/6 inhibitor with aromatase inhibitor (AI) as initial therapy for advanced disease, or
  • On/after treatment with a CDK4/6 inhibitor plus endocrine therapy (ET) administered as adjuvant therapy for early stage breast cancer

• Must be deemed appropriate for treatment with ET

• If female, have a postmenopausal status by natural or surgical means or by ovarian function suppression

• Have Response Evaluable Criteria in Solid Tumors (RECIST) evaluable disease (measurable disease and/or nonmeasurable disease)

• Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group scale (Oken et al. 1982)

• Have adequate renal, hematologic, and hepatic organ function

• Must be able to swallow capsules/tablets

Exclusion Criteria:

• Have visceral crisis, lymphangitic spread, or leptomeningeal carcinomatosis
• Have symptomatic or untreated central nervous system metastasis
• Have received any systemic therapy between disease recurrence/progression and study screening
• Have received more than 1 line of therapy for advanced or metastatic disease.
• Have received prior chemotherapy for metastatic breast cancer (MBC)
• Have received prior treatment with fulvestrant, any investigational estrogen receptor (ER)-directed therapy (including selective ER degraders [SERDs] and non-SERDs), any phosphatidylinositol 3-kinase (PI3K)-, mammalian target of rapamycin (mTOR)-, or protein kinase B (AKT)-inhibitor

Anonymized individual patient level data will be provided in a secure access environment upon approval of a research proposal and a signed data sharing agreement.

Data are available 6 months after the primary publication and approval of the indication studied in the US and European Union (EU), whichever is later. Data will be indefinitely available for requesting.

A research proposal must be approved by an independent review panel and researchers must sign a data sharing agreement.