CyclinD1 Is Useful to Differentiate Langerhans Cell Histiocytosis From Reactive Langerhans Cells

Langerhans cell histiocytosis (LCH) is a rare histiocytic disorder characterized by clonal proliferation of neoplastic Langerhans cells (LCs). LC proliferation can also be seen in different reactive dermatosis. CyclinD1 is a downstream marker of mitogen-activated protein (MAP) kinase pathway, which is often activated in LCH. This study aimed to evaluate the role of cyclinD1 to differentiate reactive LC proliferation from LCH. All cases of cutaneous LCH diagnosed by biopsy in the past 3 years (n = 13) were immunostained with CD1a, p53, CD31, and cyclinD1. Seven cases each of discoid lupus erythematosus (DLE) and lichen planus (LP) were taken as control. Presence of p53, CD31, and cyclinD1-positive LCs (CD1a-positive) were compared in the dermis. In all LCH cases, dermal neoplastic LCs showed diffuse CD1a positivity and 12 cases (92.3%) showed variable (30%-70%) cyclinD1 expression. Weak p53 and CD31 expression were seen in 61.5% and 46.1% of LCH cases, respectively. In the control group, 5 cases of LP and 4 cases of DLE showed variable LC proliferation, highlighted by CD1a positivity. However, no case of reactive dermatosis showed cyclinD1 or p53 expression by the reactive LCs. Weak and patchy CD31 expression by the reactive LCs were found in 1 (25%) and 2 (40%) cases of DLE and LP, respectively. To conclude, cyclinD1 is frequently expressed in neoplastic LCs in LCH. It is an efficient marker to differentiate neoplastic from reactive LC proliferation, and can be used as a surrogate marker in LCH.