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Background We report results from the phase I dose-finding and phase II expansion part of a multicenter, open-label study of single-agent lenvatinib in pediatric and young adult patients with relapsed/refractory solid tumors, including osteosarcoma and radioiodine-refractory differentiated thyroid cancer (RR-DTC) (NCT02432274). Patients and methods The primary endpoint of phase I was to determine the recommended phase II dose (RP2D) of lenvatinib in children with relapsed/refractory solid malignant tumors. Phase II primary endpoints were progression-free survival rate at 4 months (PFS-4) for patients with relapsed/refractory osteosarcoma; and objective response rate/best overall response for patients with RR-DTC at the RP2D. Results In phase I, 23 patients (median age, 12 years) were enrolled. With lenvatinib 14 mg/m2, three dose-limiting toxicities (hypertension, n = 2; increased alanine aminotransferase, n = 1) were reported, establishing 14 mg/m2 as the RP2D. In phase II, 31 patients with osteosarcoma (median age, 15 years) and 1 patient with RR-DTC (age 17 years) were enrolled. For the osteosarcoma cohort, PFS-4 (binomial estimate) was 29.0% [95% confidence interval (CI) 14.2% to 48.0%; full analysis set: n = 31], PFS-4 by Kaplan–Meier estimate was 37.8% (95% CI 20.0% to 55.4%; full analysis set) and median PFS was 3.0 months (95% CI 1.8-5.4 months). The objective response rate was 6.7% (95% CI 0.8% to 22.1%). The patient with RR-DTC had a best overall response of partial response. Some 60.8% of patients in phase I and 22.6% of patients in phase II (with osteosarcoma) had treatment-related treatment-emergent adverse events of grade ≥3. Conclusions The lenvatinib RP2D was 14 mg/m2. Single-agent lenvatinib showed activity in osteosarcoma; however, the null hypothesis could not be rejected. The safety profile was consistent with previous tyrosine kinase inhibitor studies. Lenvatinib is currently being investigated in osteosarcoma in combination with chemotherapy as part of a randomized, controlled trial (NCT04154189), in pediatric solid tumors in combination with everolimus (NCT03245151), and as a single agent in a basket study with enrollment ongoing (NCT04447755)., Highlights • The recommended phase II dose of lenvatinib in children with relapsed/refractory solid malignant tumors is 14 mg/m2. • This dose is equivalent to the recommended dose of 24 mg/day for single-agent lenvatinib in adults with DTC. • Single-agent lenvatinib showed activity of interest in children and young adults with osteosarcoma. • Based on this initial report, lenvatinib is currently being investigated in combination with chemotherapy in osteosarcoma.

Background Lenvatinib (LEN) is a multikinase inhibitor of VEGFR1–3 and other targets. We report data from phase Ib dose-finding and phase II expansion cohorts of LEN + etoposide + ifosfamide in pts with r/r osteosarcoma. Methods Pts were aged 2 to ≤ 25 years with r/r osteosarcoma and Results In the phase Ib dose-finding cohort (n = 22), pts received LEN 11 mg/m2 (n = 7) and 14 mg/m2 (n = 15) + chemo. Dose-limiting toxicities were: Grade (G) 4 thrombocytopenia (n = 1; LEN 11 mg/m2), G4 thrombocytopenia and G3 epistaxis (n = 1; LEN 14 mg/m2), G2 oral dysesthesia, G3 muscle spasm, and G2 back pain (n = 1; LEN 14 mg/m2). RPh2D was LEN 14 mg/m2 + chemo. In the expansion cohort (n = 20), the median number of LEN cycles received was 4 (range: 1–7). As reported in the database, the most frequent treatment-emergent adverse events (TEAEs) were platelet count decreased/thrombocytopenia (50%/30%), neutropenia/neutrophil count decreased (45%/25%), anemia (45%), nausea (40%), ALT increased, diarrhea, and white blood cell count decreased (30% each). Most frequent G ≥ 3 TEAEs were neutropenia/neutrophil count decreased (45%/25%), platelet count decreased/thrombocytopenia (40%/20%), white blood cell count decreased (30%), and anemia (25%). Pneumothorax was observed in the dose-finding cohort (n = 6) and expansion cohort (n = 1); 2 (dose-finding cohort) were ≥G3; and 1 was post-thoracotomy. 4 Pts (dose-finding cohort) discontinued treatment due to TEAEs. There were no treatment-related fatal serious AEs. In the dose-finding combination cohort, 12/18 evaluable pts (66.7%) achieved PFS-4. In the phase II expansion cohort, 5/8 evaluable pts (62.5%) achieved PFS-4. Conclusions The combination of RPh2D LEN (14 mg/m2) + chemo had a manageable safety profile with promising preliminary evidence of efficacy. Clinical trial identification NCT02432274. Legal entity responsible for the study Eisai Inc. Funding Eisai Inc. Disclosure A. Longhi: Non-remunerated activity/ies, non-financial support: PharmaMar, Takeda; Research grant / Funding (institution): Takeda. M. Casanova: Advisory / Consultancy, advisory role: Bayer; Advisory / Consultancy, advisory role: Lilly; Advisory / Consultancy, advisory role: Roche; Advisory / Consultancy, advisory role: Tesaro. S.S. Bielack: Travel / Accommodation / Expenses, site fees for study preparation: Eisai; Travel / Accommodation / Expenses, personal fees from Clinigen: Clinigen; Travel / Accommodation / Expenses, personal fees from Lilly: Lilly; Travel / Accommodation / Expenses, personal fees from Novartis: Novartis; Travel / Accommodation / Expenses, personal fees from Bayer: Bayer; Travel / Accommodation / Expenses, personal fees from Pfizer: Pfizer; Travel / Accommodation / Expenses, personal fees from Isofol: Isofol; Travel / Accommodation / Expenses, personal fees from Sensorion: Sensorion; Travel / Accommodation / Expenses, personal fees from Ipsen: Ipsen; Advisory / Consultancy, Institution negotiating consultancy agreement with Eisai: Eisai. S. Gallego Melcon: Travel / Accommodation / Expenses: Loxo Oncology; Advisory / Consultancy: Bayer, Eusa. All other authors have declared no conflicts of interest.