PROOF 301: Results of an early discontinued randomized phase 3 trial of the oral FGFR inhibitor infigratinib vs. gemcitabine plus cisplatin in patients with advanced cholangiocarcinoma (CCA) with an <i>FGFR2</i> gene fusion/rearrangement.

516 Background: Infigratinib (BGJ398), an oral inhibitor of fibroblast growth factor receptor (FGFR)1-3 with demonstrated clinical activity and a manageable adverse event profile in a phase 2 study in patients with previously treated, unresectable or metastatic CCA with an FGFR2 fusion or other rearrangement, represented one of the few targeted treatment options after progression on first-line therapy, as per FDA conditional approval. The confirmatory phase III trial PROOF 301 of infigratinib versus gem/cis as frontline treatment of FGFR2 Gene Fusions/Translocations CCA was early discontinued. Here we report the efficacy and safety in the patients accrued prior to termination. Methods: Eligible patients were randomized 2:1 to infigratinib 125 mg on days 1-21 of a 28-day cycle vs intravenous gemcitabine (1000 mg/m 2 ) + cisplatin (25 mg/m 2 ) on days 1 and 8 of a 21-day cycle. The primary endpoint was progression-free survival (PFS), confirmed by blinded independent central review (BICR). Secondary endpoints included overall survival (OS), investigator determined PFS, overall response rate (ORR), best overall response (BOR), disease control rate (DCR), duration of response (DOR), and safety and tolerability. Crossover to the investigational arm was permitted at progression. Results: Over 40 months, a total of 1127 patients were pre-screened at 120 sites and 48 enrolled. In a 2:1 randomization, 29 patients received infigratinib and 19 received gem/cis. Upon progression, 2 patients crossed over from gem/cis to infigratinib. Median PFS (95% CI) by BICR was 7.4 (5.4, not evaluable [NE]) and 8.0 (3.4, NE) months with infigratinib and chemotherapy, respectively. The ORRs by BICR were 37.9 % with infigratinib and 15.8 % with gem/cis. Grade 3–4 adverse events occurred in 79.3% and 58.8% patients treated with infigratinib and chemotherapy. Conclusions: Infigratinib showed a preliminary signal of efficacy in the first-line treatment of FGFR2-rearranged CCA, but due to early termination of the study, the power is insufficient to draw conclusions regarding its efficacy in comparison to gem/cis. This study highlights the challenge of performing confirmatory studies in biomarker-selected subpopulations of rare tumors and the importance of exploring alternative approaches to delivering confirmatory data for regulatory purposes. Clinical trial information: NCT03773302 .