Modified LCH-III Regimen With or Without Luvometinib for Multisystem Pediatric Langerhans Cell Histiocytosis

Condition(s) studied

Investigational drug(s) / intervention(s)

Prednisone: Corticosteroid administered orally as part of the modified LCH-III regimen

Vincristine: Intravenous vinca alkaloid chemotherapy agent used in the modified LCH-III regimen

Mercaptopurine: Oral purine analog antimetabolite used in the maintenance phase of therapy for multisystem LCH

Luvometinib: Oral selective MEK1/2 inhibitor added to the experimental arm. Administered daily in combination with modified LCH-III chemotherapy for multisystem Langerhans cell histiocytosis.

Study summary

Langerhans cell histiocytosis (LCH) is the most common histiocytic disorder in children, caused by excessive proliferation and accumulation of Langerhans cells (a type of immune cell) in various body tissues. The annual incidence is about 2.6-8.9 cases per million children.Clinical presentation varies widely.

Mild (low-risk) cases may resolve spontaneously or cause minimal issues with excellent outcomes. Severe multisystem LCH involves multiple organs, particularly high-risk sites such as liver, spleen, or bone marrow, leading to poorer prognosis and potential life-threatening complications without appropriate treatment.Standard first-line therapy for many children is prednisone (a corticosteroid) plus vinblastine (chemotherapy). Trials like LCH-III show near-100% survival in low-risk disease, but long-term survival drops to \~80% in high-risk cases. Reactivation occurs in \~37% of low-risk patients post-treatment, and \~50% of children eventually develop resistance, resulting in progression or relapse. Treatment failure heightens risks of long-term sequelae, including growth retardation, endocrine dysfunction, and neurological damage, severely impacting quality of life.

More than half of LCH cases harbor the BRAF V600E mutation, activating the MAPK pathway abnormally. This has driven development of targeted MAPK inhibitors (e.g., vemurafenib, dabrafenib, trametinib), which demonstrate strong efficacy and acceptable safety (mainly manageable skin rash) in relapsed/refractory pediatric cases, with no reported secondary malignancies to date. These agents provide rapid symptom relief and durable control, though monotherapy often fails to eradicate abnormal cells in multisystem disease, leading to relapse after discontinuation.

No MAPK inhibitors were previously approved specifically for LCH. In 2025, luvometinib (developed by Fosun Pharma, China; a selective MEK1/2 inhibitor) received approval in China for adult LCH and histiocytic neoplasms. Adult studies showed \~83% objective response rate and \~74% progression-free at ≥12 months, with mostly mild side effects (skin issues, hypertriglyceridemia) and no discontinuations due to serious toxicity.

Laboratory evidence indicates MAPK overactivation confers apoptosis resistance to LCH cells; combining MAPK inhibitors with chemotherapy may enhance cell killing and leverage chemotherapy-induced immune microenvironment changes for better clearance.

Small studies and real-world data in refractory LCH support this: combination regimens yielded low relapse rates (especially with prolonged therapy), 100% responses in some pediatric cohorts with sustained remission and no added severe toxicity, and notably lower relapse (20% vs 75% with inhibitor alone) in our center's early experience with LCH-III backbone plus MAPK inhibitor.

This multicenter randomized trial will enroll children with multisystem LCH, assigning them to modified standard LCH-III chemotherapy alone or the same regimen combined with luvometinib, to evaluate whether adding this targeted agent improves outcomes.

Eligibility

Primary outcome measure(s)

• Event-Free survival rate — From Day 1 until the date of first event or last follow-up, assessed up to 2 years.
  Event-free survival (EFS) is defined as the time from Day 1 to the first occurrence of any event, including disease reactivation , second primary malignancy, or death from any cause. Events will be assessed by clinical examination, imaging, and laboratory tests. The 2-year EFS rate will be estimated using the Kaplan-Meier method, reported as percentage with 95% confidence interval.

Trial sites (11)

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