The top altered genes were TP53 (44%), ESR1 (37%), CDH1 (17%), FGFR1 (12%), NF1 (11%), CHEK2 (10%), and PTEN (9%). In pts treated with PBO+FUL, alterations in PTEN (HR 2.8; 95% CI 1.4-5.7; p=0.0107) and TP53 (HR 2.0; 95% CI 1.3-3.1; p=0.0025) were associated with a worse prognosis compared to pts with no mutation detected (NMD) in these genes. In pts treated with TAS+FUL, alterations in FGFR1 (HR 2.4; 95% CI 1.5-3.7; p=0.0006), TP53 (HR 1.9; 95% CI 1.4-2.6; p=0.0001) and PTEN (HR 1.8; 95% CI 1.1-2.8; p=0.0265) were associated with a worse prognosis compared to pts with NMD in these genes.We report that the most frequently mutated genes identified are consistent with previous studies in pts with ER+, HER2- aBC. This analysis shows that alterations in TP53 and PTEN were associated with poor prognosis in both tx arms, and FGFR1 alterations were associated with a poor prognosis in TAS+FUL treated pts. Further, NF1 alterations were associated with a poor prognosis in PBO+FUL treated pts, an association that was not observed with TAS+FUL.