Abstract
TPS1148 Background: Overcoming endocrine resistance is a critical goal in the treatment of hormone receptor−positive (HR+) breast cancer. Molecular mechanisms associated with endocrine resistance include adaptive “cross-talk” between the estrogen receptor and the fibroblast growth factor receptor (FGFR). Up to 8% of HR+/HER2- breast cancer patients (pts) have amplification of the FGFR1 gene, which is associated with resistance to endocrine therapy but can be overcome via FGFR1 inhibition in preclinical models. Dovitinib is a potent FGF, VEGF, and PDGF receptor tyrosine kinase inhibitor that demonstrated antitumor activity in heavily pretreated breast cancer pts with FGF pathway amplification (FGFR1, FGFR2, or ligand FGF3; Andre et al, ASCO 2011). Dovitinib may reverse resistance to endocrine therapy related to FGF-pathway amplification and is studied here to determine if it can improve outcomes when combined with fulvestrant. Methods: Postmenopausal HER2-/HR+ locally advanced or metastatic breast cancer pts (N»150) progressing within 12 months of completion of adjuvant endocrine therapy or after ≤ 1 prior endocrine therapy in the advanced setting will be enrolled in this multicenter, randomized, double blind, placebo controlled, phase II trial. Pts will prospectively undergo molecular screening to enrich for FGF-amplification (FGFR1, FGFR2, or FGF3 amplification by qPCR; 45 amplified and 30 non-amplified pts per arm). Pts will be randomized 1:1 to receive fulvestrant (500 mg q4w [with an additional dose 2 wks after the initial dose]) in combination with oral dovitinib (500 mg, 5 days on/2 days off) or placebo until disease progression, unacceptable toxicity, or death. The primary endpoint is progression-free survival, with tumor assessments performed q8w. Secondary endpoints include overall response rate per RECIST v1.1, duration of response, overall survival, ECOG performance status and patient reported outcome scores over time, and safety. The pharmacodynamic effect of dovitinib on FGFR-associated angiogenic pathways in tumor specimens and potential predictive biomarkers of response to dovitinib will be explored.
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