Characteristic features of LCH in adults
| Clinical and radiographic features |
| 1. Upper lobe predominant nodular and cystic lung lesions in a smoker |
| 2. Central diabetes insipidus |
| 3. Punched-out lytic osseous lesions, often involving flat bones (skull, sternum, ribs, pelvis) |
| Histopathologic features |
| 1. Lesional histiocytes with elongated, grooved nuclei, often with intermixed eosinophils |
| 2. CD207 (langerin)- and CD1a-positive histiocytes in lesional tissue by IHC |
| 3. Characteristic pattern of tissue involvement to exclude reactive Langerhans cells |
| Molecular features |
| 1. BRAF-V600E mutation |
| 2. Other activating mutations in the RAS-RAF-MEK-ERK pathway (MAP2K1, BRAF, KRAS, NRAS, ARAF, etc) |
| 3. Activating kinase fusions |
| Clinical and radiographic features |
| 1. Upper lobe predominant nodular and cystic lung lesions in a smoker |
| 2. Central diabetes insipidus |
| 3. Punched-out lytic osseous lesions, often involving flat bones (skull, sternum, ribs, pelvis) |
| Histopathologic features |
| 1. Lesional histiocytes with elongated, grooved nuclei, often with intermixed eosinophils |
| 2. CD207 (langerin)- and CD1a-positive histiocytes in lesional tissue by IHC |
| 3. Characteristic pattern of tissue involvement to exclude reactive Langerhans cells |
| Molecular features |
| 1. BRAF-V600E mutation |
| 2. Other activating mutations in the RAS-RAF-MEK-ERK pathway (MAP2K1, BRAF, KRAS, NRAS, ARAF, etc) |
| 3. Activating kinase fusions |