Cyclin D1: potential utility as marker for Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a rare disorder of unknown etiopathogenesis. Diagnosis is based on the identification of CD1a positive histiocytic infiltrate. Activation of the mitogen-activated-protein-kinase (MAPK) is constantly observed in LCH and therefore downstream markers such as cyclin D1 may be a useful marker for LCH. The aim of this study was to investigate the expression of cyclin D1 in LCH. We assessed the immunohistochemical expression of cyclin D1 (clone SP4-R) in series of 16 cases of confirmed LCH. Expression of Cyclin D1 was scored as weak, moderate, and strong nuclear staining and results were interpreted by two pathologists. The percentage of positivity was assessed. The mean age of patients was 13.7 years old with a male to female ratio of 1:3. The most common involved site was bone (n = 9; 56,3%), followed by lymph node (n = 5; 31,2%) and skin (n = 2; 12,5%). All cases showed nuclear staining for cyclin D1 with variable intensity. It was assessed moderate in 43,8% (n = 7) and strong in 56,2% (n = 9). The percentage of positive cells was >50% in 13 cases and <50% in 3 cases. Our results have shown that all cases of Langerhans cell histiocytosis from various sites express cyclin D1. This finding may be attributed to MAPK pathway activation that has been described in LCH. Otherwise, cyclin D1 is not significantly expressed in reactive Langerhans cell proliferations. Therefore, cyclin D1 immunohistochemistry may be useful as a diagnostic marker and in excluding non-neoplastic mimics of LCH.