ESR1 and cancer: Cancers were classified into four clinically relevant treatment IHC groups by combined ER/PR status and HER2 status as follows: ER-/PR-, HER2- (n=92; 46.7%), ER-/PR-, HER2+ (n=20; 10.1%), ER+/PR+, HER2- (n=76; 38.6%) and ER+/PR+, HER2+ (n=9; 4.6%).