Bone marrow involvement of Langerhans cell histiocytosis: immunohistochemical evaluation of bone marrow for CD1a, Langerin, and S100 expression.

Aims: Although bone marrow (BM) involvement in Langerhans cell histiocytosis (LCH) is a negative prognostic indicator, there are no widely accepted criteria to define BM involvement in LCH. We evaluated the BM of LCH patients at diagnosis by immunohistochemical (IHC) staining for S100, CD1a and Langerin, along with other features.
Methods and Results: We retrospectively reviewed the records of 75 patients diagnosed as LCH at our center. IHC stains of Langerin, CD1a and S100 were done using paraffin-embedded tissue sections. Only three cases showed massive involvement of clustered Langerhans cells. There were linear associations between positive cell count and disease extent. Some discordant results between Langerin and CD1a IHC stains were noted. Among cases showing positive results for all three IHC stains, six patients (54.5%) were in the multisystem group, and three patients (27.3%) had cytopenias. The reactivation-free survival rates did not differ between the group positive for CD1a or Langerin, and the group negative for Langerin and CD1a.
Conclusions: Langerin and CD1a seem to be useful markers of Langerhans cells, and S100 might be a nonspecific marker for these cells, in the BM. Both Langerin and CD1a IHC staining is needed to evaluate the BM involvement of LCH.
(© 2014 John Wiley & Sons Ltd.)