Exploratory biomarker analyses suggested that pts with high FGFR1 amplification (FGFR1/centromere ratio >4 , n = 16) presented higher ORR than those without high level amplification (n = 37) (25% versus 8%). ORR in pts with FGFR1-high tumors (IHC, H-score >50) was 25% (n = 5/20) while ORR was 8% in FGFR1-low cancers. The 20 patients with FGFR1 membrane over-expression had in average 3-month longer PFS (212[165-NA] days) than other patients (109[57-158] days). Serum FGF23 levels after 14 days of lucitanib were significantly increased from baseline (p < 0.0001), suggesting an effective targeting on FGFR...the FINESSE trial suggests that lucitanib has antitumor activity in pts with HR+ HER2- MBC. Biomarker analyses generates the hypothesis that pts with high FGFR1 expression could derive more benefit.