postMONARCH: A Randomized, Double-Blind, Placebo-Controlled, Phase 3 Study to Compare the Efficacy of Abemaciclib plus Fulvestrant to Placebo plus Fulvestrant in Participants with HR+, HER2-, Advanced or Metastatic Breast Cancer Following Progression on a CDK4 & 6 Inhibitor and Endocrine Therapy

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