A multicenter, open-label phase II trial of dovitinib, a fibroblast growth factor receptor 1 (FGFR1) inhibitor, in FGFR1-amplified and nonamplified metastatic breast cancer (BC).

Abstract

289 Background: Amplification of the FGFR1 gene occurs in ≈ 10% of BC, correlates with FGFR1 overexpression, and is mainly observed in estrogen receptor (ER)-positive human epidermal growth factor receptor 2 (HER2)- BCs. Dovitinib (TKI258) is a multitargeted tyrosine kinase inhibitor that demonstrated potent antitumor activities in FGFR1-amplified tumor cell lines. This phase 2 study evaluated the efficacy and safety of dovitinib in metastatic HER2- BC. Methods: Patients were stratified into 4 groups based on FGFR1 and hormone receptor (HR) tumor subtype: 1) FGFR1+, HR+; 2) FGFR1+, HR-; 3) FGFR1-, HR+; 4) FGFR1-, HR-. Screening for FGFR1 status was performed by fluorescence/chromogenic in situ hybridization (cutoff ≥ 6 gene copies). Dovitinib (500 mg) was administered once daily on a 5-day-on/ 2-day-off schedule. The primary endpoint was RECIST best overall response rate in patients with measurable disease per external radiology review. Results: Data from 77 of 81 treated patients were available as of January 2011 (n=21, n=34, n=22 in groups 1, 3, 4, respectively). Median number of prior therapies in the metastatic setting was 2 chemotherapy lines (all patients) and 2 endocrine therapy lines (HR+ patients). Liver metastases were present in 58% of patients (81%, 50%, 50% in groups 1, 3, 4, respectively). Most common adverse events included vomiting (75%; grade 3 [g3]: 6%), diarrhea (72%; g3: 6%), nausea (62%; g3: 5%), and asthenia (61%; g3: 17%). Median dovitinib exposure was 1.7 (range, 0-8.2) months, including 8 patients with > 4 months of therapy. Of patients with measurable disease at baseline, in group 1, 13% had unconfirmed partial responses and 44% had stable disease ≥ 4 months (SD4). In groups 3 and 4, 29% and 11% had SD4. Conclusions: This is the first trial reporting efficacy of an FGFR1 inhibitor in patients with FGFR1-amplified BC. Dovitinib showed antitumor activity in patients with HR+, FGFR1- amplified BC and disease stabilization in other subgroups. FGFR1 is likely a relevant target in BC, and FGFR1 amplification may define a segment of dovitinib-sensitive disease. Further evaluation of dovitinib in patients with HR+ BC is planned.