The main purpose of this study is to examine the side effects that participants with metastatic breast cancer experience when taking abemaciclib with or without food.

Inclusion Criteria:

• Have a diagnosis of HR+, HER2- metastatic breast cancer (mBC).

• Have all of the following:

  • Recurrent, locally advanced, unresectable or mBC with disease progression following anti-estrogen therapy.
  • Prior treatment with chemotherapy for locally advanced or metastatic disease.
  • No prior treatment with cyclin-dependent kinases (CDK) 4 and 6 inhibitor.

• Have Eastern Cooperative Oncology Group performance status (ECOG PS) ≤1.

• Have discontinued all previous treatments for cancer and recovered from the acute effects of therapy.

• Have adequate organ function.

• Women of child-bearing potential must have a negative pregnancy test.

• Are able to swallow tablets/capsules.

Exclusion Criteria:

• Are currently receiving treatment in a clinical study involving an investigational product.
• Have a serious concomitant systemic disorder.
• Have symptomatic central nervous system (CNS) malignancy or metastasis.
• Have a symptomatic Human Immunodeficiency Virus (HIV) infection or symptomatic activated/reactivated hepatitis A, B, or C.
• Have a personal history of syncope of either unexplained or cardiovascular etiology, ventricular tachycardia, ventricular fibrillation, or sudden cardiac arrest.
• Have a history of any other cancer.
• Had major surgery within 14 days prior to randomization.
• Are breastfeeding.
• Have received treatment with a drug that has not received regulatory approval for any indication within 14 or 21 days of the initial dose of study drug for a nonmyelosuppressive or myelosuppressive agent, respectively.

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 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.