ESR1 and breast cancer: Among TNBC stage I-III (N = 321) and stage IV (N = 216) breast cancers, the most frequent alterations were mutations in PIK3CA (19.9% vs 21.3%), BRCA1/2 (11.5% vs 12.0%), ESR1 (0.31% vs 0%), PALB2 (0.9% vs 1.4%), and PD-L1 amplification (2.2% vs 4.6%).