This protocol addresses the management of unifocal Langerhans cell histiocytosis — a single lesion involving any organ — in adult patients without diabetes insipidus.
LCH classification distinguishes unifocal disease (a solitary lesion) from multifocal single-system disease. In adults without diabetes insipidus, the approach typically begins with observation or local measures such as surgical excision, intralesional steroids, or radiation. This protocol applies when systemic management becomes relevant.
When systemic therapy is warranted, the protocol includes targeted options selected according to the molecular profile of the disease. The full regimen — specific agents, selection criteria, and clinical algorithm — is available in the complete protocol.
Disease response is assessed using FDG-PET-based imaging, evaluated after an initial period of therapy.
DOI: 10.1182/blood.2021014343
The proposed classification system differentiates between unifocal (solitary lesion) and single-system multifocal disease (>1 lesion).
For unifocal LCH (except DI), observation or local therapies such as surgical excision, intralesional steroids, or radiation are recommended as first-line treatments.
For LCH refractory to first-line treatment or with end-organ dysfunction (e.g., neurologic impairment, sclerosing cholangitis), alternate conventional treatment or targeted therapies (BRAF or MEK inhibitors) should be implemented.
For disease that is relapsed or refractory following chemotherapy, it is reasonable to consider an alternate chemotherapy agent or a kinase inhibitor based on patient-specific factors and drug availability.
Because most patients will require a dose reduction and lower doses of BRAF and MEK inhibitors are quite effective, it is reasonable to start at half of the dose currently used to treat patients with melanoma.
For initially FDG PET avid LCH, it is recommended to repeat an FDG PET-based imaging study for assessment of disease response after 2–3 months of initiation of therapy, with subsequent imaging frequency tailored individually based on the specific clinical scenario.
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