Risk groups as defined by the Langerhans Cell Histiocytosis–III Protocol.
| Group 1: Multisystem “risk” patients |
| Multisystem patients with involvement of 1 or more “risk” organs (i.e., hematopoietic system, liver, spleen, or lungs). Patients with single-system lung involvement are not eligible for randomization. |
| Group 2: Multisystem “low-risk” patients |
| Multisystem patients with multiple organs involved but without involvement of “risk” organs. |
| Group 3: Single-system “multifocal bone disease” and localized “special site” involvement |
| Patients with multifocal bone disease—that is, lesions in 2 or more different bones. Patients with localized special site involvement, such as “central nervous system risk” lesions with intracranial soft tissue extension or vertebral lesions with intraspinal soft tissue extension. |
| Group 1: Multisystem “risk” patients |
| Multisystem patients with involvement of 1 or more “risk” organs (i.e., hematopoietic system, liver, spleen, or lungs). Patients with single-system lung involvement are not eligible for randomization. |
| Group 2: Multisystem “low-risk” patients |
| Multisystem patients with multiple organs involved but without involvement of “risk” organs. |
| Group 3: Single-system “multifocal bone disease” and localized “special site” involvement |
| Patients with multifocal bone disease—that is, lesions in 2 or more different bones. Patients with localized special site involvement, such as “central nervous system risk” lesions with intracranial soft tissue extension or vertebral lesions with intraspinal soft tissue extension. |