CCND1 gene amplification was associated with shorter progression-free survival (PFS) in patients receiving aromatase inhibitors (AI) [16.0 months vs. 32.4 months, HR = 3.16 (95% CI 1.26-7.93), p = 0.014]. Presence of CCND1 and/or FGFR1 amplification is associated with worse outcomes of AI therapy in patients with metastatic BC.