Background: LEN inhibits the activity of vascular endothelial growth factor receptor, fibroblast growth factor receptor, and platelet-derived growth factor receptor–α. These targets have been shown to be expressed in patients (pts) with BTC. The objective of this study is to evaluate LEN as a potential treatment option for these pts. Methods: This is an open-label, phase 2 study conducted in Japan. Pts aged ≥ 20 years with confirmed diagnosis of unresectable BTC, measureable disease per Response Evaluation Criteria in Solid Tumors v1.1, and 1 prior gemcitabine-based doublet chemotherapy, will receive LEN 24 mg/d. The primary endpoint is objective response rate. Secondary objectives include disease control rate (DCR), safety, and pharmacokinetics. Enrollment of 25 pts is planned. The study includes an interim evaluation for futility. If there is no objective response and disease control is achieved in < 5 pts of 15‒17 pts, the study will end. Results: An interim evaluation was performed with 17 pts enrolled (data cutoff: 25 July 2016). Ten (59%) pts were aged < 65 years, 10 (59%) were male, 2 (12%) had prior surgery, and 13 (76%) received prior gemcitabine + cisplatin therapy. Efficacy results appear in the table. One pt had a partial response (PR) and 13 had stable disease (SD). The DCR was 82%. All pts experienced treatment-emergent adverse events (TEAEs). Grade ≥ 3 TEAEs occurred in 11 (65%) and serious AEs (SAEs) occurred in 7 (41%) pts. There were no fatal SAEs. TEAEs leading to LEN discontinuation, dose reduction, and dose interruption occurred in 1 (6%), 12 (71%), and 9 (53%) pts, respectively. Analysis of trough plasma concentration in 13 pts from this study showed no difference versus that observed in a previous phase 3 study of LEN in differentiated thyroid cancer. Conclusions: Because results of this interim evaluation did not meet futility criteria, the study was continued, with findings suggesting possible activity of LEN in pts with unresectable BTC who failed gemcitabine-based doublet chemotherapy. Toxicities were generally manageable with dose modifications as only 1 pt required discontinuation from LEN. Clinical trial information: NCT02579616