Table 2 The differential diagnosis of ALK-positive histiocytosis with different entity
Entity | Mutation style | Positive marker in IHC | Morphologic features | Negative marker in IHC |
|---|---|---|---|---|
ECD | KIF5B-ALK fusion, the uncommon BRAF V600E mutation | CD68, CD163 | Foamy histiocytes with small nuclei and Touton giant cells | CD1a, positive S100 in some histiocytes, langerin, |
JXG | KIF5B-ALK fusion | S100, CD11c, CD4 | Touton giant cells, oval nuclei in foamy histiocytes | CD1a, |
RDD | Mutations in the RAS pathway | S100, CD68 | Round nuclei, vesicular chromatin, distinct Nucleoli | CD 1a |
LCH | BRAF V600E mutation in t 50– 65% of patients | S-100, CD1a, CD207 | Nuclear convolutions, vesicular nuclei, large cytoplasm | CD68, CD163 |
ALK-positive histiocytosis | KIF5B-ALK fusion | ALK, CD68, CD163, XIIIa, | Large epithelioid cells, Touton-like giant cells, absence of substantial atypia | CD1a, BRAFV600E, GFAP |