Denosumab for the Treatment of Adult LCH

Inclusion Criteria: * Adults (\>18 years of age) * Definitive diagnosis of LCH \[Based on clinic-pathological evidence with microscopic examination and at least one of the following immunological staining: Langerin (CD 207) positivity, Cluster of Differentiation 1a (CD1a) positivity, Presence of Birbeck granules on electronic microscopy\] * Mild symptoms (symptoms of low intensity; no need for hospitalization) and low risk disease needing first line systemic therapy for LCH because of: * single system disease with multifocal lesions, or * single system disease with "special site" lesions (vertebral lesions with intraspinal extension, craniofacial bone lesions with soft tissue extension), or * multi-system disease without involvement of risk organs \[hematopoietic system, spleen, liver, tumorous central nervous system (CNS)\]. * Have signed the informed consent form (consent should be taken before any study-specific procedure is performed). * A patient should undergo a PET-CT imaging test, in order for him to be deemed suitable for the study. The initial PET-CT either may have been carried out, within 3 months prior to visit 1, regardless of the diagnostic center or the type of the device, which has been used for, or may take place in the context of visit 2, at the diagnostic center(s) specialized on Nuclear Medicine, which have been partnered with the Sponsor. Whichever is the case, the initial PET-CT report should be legible and accurate, so that to be assessed by th…