Macrophage Disorders

Question 1

Answer 1

Langerhans cell histiocytosis

Note the key features:
* Lesional cells have abundant eosinophilic cytoplasm and indistinct borders
* Lesional cell nuclei have a coffee-bean groove and vesicular chromatin with small nucleoli
* Cells are accompanied by an eosinophilic infiltrate

Staining profile:
Langerin/CD207+, S100+, CD1a+. Often BRAF V600E +.

Molecular:
RAS-MAPK alterations, most commonly BRAF V600E or a MAP2K1 variant.