Giredestrant is taken orally once per day on Days 1-28 of each 28-day treatment cycle.
Giredestrant-matched Placebo
Droga
Giredestrant-matched placebo is taken orally once per day on Days 1-28 of each 28-day treatment cycle.
Letrozole 2.5 milligrams (mg) is taken orally once per day on Days 1-28 of each 28-day treatment cycle.
Letrozole-matched Placebo
Droga
Letrozole-matched placebo is taken orally once per day on Days 1-28 of each 28-day treatment cycle.
Palbociclib 125 mg is taken orally once per day on Days 1-21 of each 28-day treatment cycle.
Only premenopausal/perimenopausal and male participants will receive a luteinizing hormone-releasing hormone (LHRH) agonist on Day 1 of each 28-day treatment cycle. The investigator will determine and supply the appropriate LHRH agonist locally approved for use in breast cancer.