ESR1 and breast cancer: To inform therapeutic strategies for AI refractory patients, we evaluated co-occurring alterations with ESR1 GAs and identified concurrent GAs that have been associated with responses to targeted therapy in BC [4] including PIK3CA (35%), FGFR1 (16%), ERBB2 (8%), BRCA1/2 (5%), and AKT1 (4%) (Figure 2F).