Response-adapted Luvometinib With or Without Cytarabine in Langerhans Cell Histiocytosis

This single-center, prospective, interventional phase 2 study evaluates a response-adapted treatment strategy for patients aged 10 years and older with histologically confirmed Langerhans cell histiocytosis requiring systemic therapy. All participants receive six 35-day cycles of luvometinib induction. Post-induction treatment follows the cycle 6 PET/CT response: participants with complete metabolic response continue luvometinib maintenance without cytarabine, whereas participants without complete metabolic response who are judged suitable to continue protocol treatment receive luvometinib plus cytarabine followed by luvometinib maintenance; participants with progression or otherwise unsuitable to continue protocol treatment may receive other standard therapy or discontinue study treatment per protocol. The primary endpoint is objective response rate after six cycles by blinded independent central review.

Inclusion Criteria: * Histologically confirmed Langerhans cell histiocytosis (LCH). * Age 10 years or older. * Systemic treatment indication and at least one PET response criteria-evaluable lesion. * Expected survival of at least 12 weeks, as judged by the investigator, and able to undergo protocol-specified treatment, assessments, and follow-up. * ECOG performance status 0-2 or Lansky score \>=60. * Adequate organ function as defined in the protocol. * Written informed consent from adult participants or legal guardians, with participant assent when applicable. Exclusion Criteria: * Hypersensitivity to luvometinib or any excipient. * Concurrent other malignant tumor. * Pregnancy or breastfeeding. * Failure to meet protocol contraception requirements. * Active bacterial, fungal, or viral infection. * Significant retinal disease or glaucoma. * NYHA class \>=3 heart failure or LVEF \