To Evaluate the Efficacy, Safety, and PK Characteristics of FCN-159 in Pediatric Patients With Refractory/Recurrent LCH

Inclusion criteria

• ✓. Age 2-16 (inclusive)
• ✓. Patients with histologically confirmed Langerhans cell histiocytosis (LCH) diagnosed by the central laboratory.
• ✓. If sufficient tumor tissue samples and peripheral blood samples are available, central laboratory biomarker testing is required as follows: including but not limited to ERBB3, BRAF, ARAF, HRAS, KRAS, NRAS, MEK (MAP2K1 and MAP2K2), and other MEK upstream genes.If inability to get tissue, the gene testing results from a local laboratory also can be accepted.
• ✓. Patients who have received at least prior first-line systemic treatment, defined as treatment including vinblastine (VBL) and glucocorticoids for at least 2 weeks. VBL can be substituted with vincristine (VCR) or vindesine (VDS). Alternatively, patients may be unable to tolerate chemotherapy due to severe chemotherapy toxicity. Inability to tolerate chemotherapy is defined as one of the following: Severe liver impairment (liver enzyme elevation ≥ 5 × upper limit of normal (ULN) and bilirubin elevation ≥ 1.5 × ULN), severe neurotoxicity related to vinca alkaloids, chemotherapy-related intracranial hypertension, or grade 4 bone marrow depression with severe infection (sepsis, severe pneumonia, etc.) after chemotherapy.
• ✓. Refractory/relapsed LCH is defined as the presence of one of the following:
• ✓. Failure of prior treatment, i.e., no regression in risk organs after at least 2 weeks of systemic treatment, or overall evaluation of AD-progression or AD-mix;
• ✓. Initial response of the disease to first or second-line systemic treatment is NAD or AD-better or AD-stable, followed by disease reactivation after maintenance therapy for more than 3 months. Second-line treatment includes cytarabine and/or cladribine.
• ✓. Persistent mutated gene positive in plasma free DNA testing during prior treatment (confirmed by 2 consecutive tests) or retest positive after treatment discontinuation;