A Study With Tovorafenib (DAY101) as a Treatment Option for Progressive, Relapsed, or Refractory Langerhans Cell Histiocytosis

PRIMARY OBJECTIVE: I. To determine overall response rate (ORR) for children and young adults with relapsed or refractory BRAFV600E positive (cohort 1) and BRAFV600E negative (cohort 2) Langerhans cell histiocytosis (LCH) treated with tovorafenib (DAY101) after 2 cycles and must be maintained 4 weeks later. SECONDARY OBJECTIVES: I. To determine nature and severity of adverse events in patients treated with tovorafenib (DAY101) for relapsed or refractory LCH. II. To describe event-free survival (EFS) at 1 year in children and young adults with relapsed and refractory LCH treated with tovorafenib (DAY 101) for up to 1 year. III. To determine durability of response in children and young adults with relapsed or refractory LCH treated with tovorafenib (DAY101) following cessation of therapy in patients with complete response (CR) at 1 year. IV. To describe progression-free (and relapse-free) survival (PFS) and overall survival (OS) in children and young adults with relapsed or refractory LCH treated with tovorafenib (DAY101) for up to 1 year. EXPLORATORY OBJECTIVES: I. To determine potential role of pathogenic tumor mutation in response to tovorafenib (DAY101), and to evaluate changes in bone marrow and peripheral blood cell populations carrying pathogenic mutations in response to tovorafenib (DAY101) therapy. Ia. To define somatic mutations in LCH lesion biopsies; Ib. To determine impact of tovorafenib (DAY101) on bone marrow and blood BRAFV600E+ mononuclear cells; Ic. To determine impact of tovorafenib (DAY101) on cerebral spinal fluid and disease response; Id. To determine the performance of standardized immunohistochemical analysis of LCH lesion biopsies. II. To compare performance of LCH-specific response criteria to Response Evaluation Criteria in Solid Tumors (RECIST) criteria. III. To describe the pharmacokinetics of tovorafenib (DAY101) when administered to pediatric and young adult patients with relapse or refractory LCH. OUTLINE: This is a dose escalation study of tovorafenib followed by a phase II trial. Patients receive tovorafenib orally (PO) once weekly (QW) on days 1, 8, 15, and 22 of each cycle. Cycles repeat every 28 days for 12 cycles in the absence of disease progression or unacceptable toxicity. Patients also undergo multi-gated acquisition (MUGA) or echocardiography (ECHO) scans, and fludeoxyglucose F-18 (FDG)-positron emission tomography (PET) or computed tomography (CT) throughout the trial, and collection of blood and urine samples on study. Patients with suspicion of bone marrow and/or central nervous system involvement will also undergo bone marrow biopsy and aspiration and lumbar puncture on study and during follow up. After completion of study treatment, patients are followed up at 28 days, months 3, 6, 9, and 12, and then at 2 years post cycle 12.