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.